mfd: Rename wm8350 static gpio_set_debounce()

The kernel already has a function with this name declared
in asm-generic/gpio.h. So if this header leaks into wm8350/gpio.c
we get

drivers/mfd/wm8350-gpio.c:40:12: error: conflicting types for 'gpio_set_debounce'
include/asm-generic/gpio.h:156:12: note: previous declaration of 'gpio_set_debounce' was here

Fix this by adding a wm8350_ prefix to the function.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>