usb: host: oxu210hp-hcd: fix gcc warning

gcc -O3 warns about correct code:

    inlined from 'oxu_hub_control.constprop' at drivers/usb/host/oxu210hp-hcd.c:3652:3:
include/linux/string.h:411:9: error: argument 1 null where non-null expected [-Werror=nonnull]
  return __builtin_memset(p, c, size);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/usb/host/oxu210hp-hcd.c: In function 'oxu_hub_control.constprop':
include/linux/string.h:411:9: note: in a call to built-in function '__builtin_memset'

Expand the code slightly to let gcc better understand it and
not warn any more.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200107214354.1008937-1-arnd@arndb.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/oxu210hp-hcd.c

@@ -2783,11 +2783,15 @@ static void ehci_port_power(struct oxu_hcd *oxu, int is_on)
 		return;
 
 	oxu_dbg(oxu, "...power%s ports...\n", is_on ? "up" : "down");
-	for (port = HCS_N_PORTS(oxu->hcs_params); port > 0; )
-		(void) oxu_hub_control(oxu_to_hcd(oxu),
-				is_on ? SetPortFeature : ClearPortFeature,
-				USB_PORT_FEAT_POWER,
-				port--, NULL, 0);
+	for (port = HCS_N_PORTS(oxu->hcs_params); port > 0; ) {
+		if (is_on)
+			oxu_hub_control(oxu_to_hcd(oxu), SetPortFeature,
+				USB_PORT_FEAT_POWER, port--, NULL, 0);
+		else
+			oxu_hub_control(oxu_to_hcd(oxu), ClearPortFeature,
+				USB_PORT_FEAT_POWER, port--, NULL, 0);
+	}
+
 	msleep(20);
 }