mfd: omap-usb-host: Remove unused linux/gpio.h

linux/gpio.h is deprecated and subject to remove.
The driver doesn't use it, simply remove the unused header.

Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/omap-usb-host.c

···
 #include <linux/delay.h>
 #include <linux/clk.h>
 #include <linux/dma-mapping.h>
-#include <linux/gpio.h>
 #include <linux/platform_device.h>
 #include <linux/platform_data/usb-omap.h>
 #include <linux/pm_runtime.h>