staging: emxx_udc: Make incorrectly defined global static

staging: emxx_udc: Make incorrectly defined global static

The global gpio_desc pointer and int vbus_irq were defined in the header,
instead put the definitions in the translation unit and make them static as
there's only a single consumer, and these symbols shouldn't pollute the
global namespace.

This fixes the following sparse warnings for this driver:
drivers/staging/emxx_udc/emxx_udc.c: note: in included file:
drivers/staging/emxx_udc/emxx_udc.h:23:18: warning: symbol 'vbus_gpio' was not
declared. Should it be static?  drivers/staging/emxx_udc/emxx_udc.h:24:5:
warning: symbol 'vbus_irq' was not declared. Should it be static?

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20210207085911.270746-1-memxor@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>