mfd: omap-usb-tll: Remove unused usbtll_readb() function

Clang with W=1 reports:

  drivers/mfd/omap-usb-tll.c:128:18: error: unused function
    'usbtll_readb' [-Werror,-Wunused-function]
  static inline u8 usbtll_readb(void __iomem *base, u32 reg)
                 ^
This function is not used so remove it.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230322125803.2570968-1-trix@redhat.com

drivers/mfd/omap-usb-tll.c

@@ -125,11 +125,6 @@ static inline void usbtll_writeb(void __iomem *base, u32 reg, u8 val)
 	writeb_relaxed(val, base + reg);
 }
 
-static inline u8 usbtll_readb(void __iomem *base, u32 reg)
-{
-	return readb_relaxed(base + reg);
-}
-
 /*-------------------------------------------------------------------------*/
 
 static bool is_ohci_port(enum usbhs_omap_port_mode pmode)