USB: Fix up terminology in include files

USB is a HOST/DEVICE protocol, as per the specification and all
documentation.  Fix up terms that are not applicable to make things
match up with the terms used through the rest of the USB stack.
Acked-by: Felipe Balbi <balbi@kernel.org>
Link: https://lore.kernel.org/r/20200701171555.3198836-1-gregkh@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/usb.h

@@ -422,7 +422,7 @@ struct usb_devmap {
  * Allocated per bus (tree of devices) we have:
  */
 struct usb_bus {
-	struct device *controller;	/* host/master side hardware */
+	struct device *controller;	/* host side hardware */
 	struct device *sysdev;		/* as seen from firmware or bus */
 	int busnum;			/* Bus number (in order of reg) */
 	const char *bus_name;		/* stable id (PCI slot_name etc) */

include/linux/usb/ch9.h

@@ -6,13 +6,13 @@
  * Wireless USB 1.0 (spread around).  Linux has several APIs in C that
  * need these:
  *
- * - the master/host side Linux-USB kernel driver API;
+ * - the host side Linux-USB kernel driver API;
  * - the "usbfs" user space API; and
- * - the Linux "gadget" slave/device/peripheral side driver API.
+ * - the Linux "gadget" device/peripheral side driver API.
  *
  * USB 2.0 adds an additional "On The Go" (OTG) mode, which lets systems
- * act either as a USB master/host or as a USB slave/device.  That means
- * the master and slave side APIs benefit from working well together.
+ * act either as a USB host or as a USB device.  That means the host and
+ * device side APIs benefit from working well together.
  *
  * There's also "Wireless USB", using low power short range radios for
  * peripheral interconnection but otherwise building on the USB framework.

include/linux/usb/gadget.h

@@ -4,7 +4,8 @@
  *
  * We call the USB code inside a Linux-based peripheral device a "gadget"
  * driver, except for the hardware-specific bus glue.  One USB host can
- * master many USB gadgets, but the gadgets are only slaved to one host.
+ * talk to many USB gadgets, but the gadgets are only able to communicate
+ * to one host.
  *
  *
  * (C) Copyright 2002-2004 by David Brownell
@@ -328,7 +329,7 @@ struct usb_gadget_ops {
 };
 
 /**
- * struct usb_gadget - represents a usb slave device
+ * struct usb_gadget - represents a usb device
  * @work: (internal use) Workqueue to be used for sysfs_notify()
  * @udc: struct usb_udc pointer for this gadget
  * @ops: Function pointers used to access hardware-specific operations.
@@ -602,7 +603,7 @@ static inline int usb_gadget_activate(struct usb_gadget *gadget)
 /*-------------------------------------------------------------------------*/
 
 /**
- * struct usb_gadget_driver - driver for usb 'slave' devices
+ * struct usb_gadget_driver - driver for usb gadget devices
  * @function: String describing the gadget's function
  * @max_speed: Highest speed the driver handles.
  * @setup: Invoked for ep0 control requests that aren't handled by