gpio: wcove: Allow return negative error code from to_reg()

The type of to_reg() is unsigned int while it might return
a negative error code. Callers are also expecting a signed type.

For sake of type consistency replace unsigned int with plain int.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/gpio/gpio-wcove.c

@@ -105,7 +105,7 @@ struct wcove_gpio {
 	bool set_irq_mask;
 };
 
-static inline unsigned int to_reg(int gpio, enum ctrl_register reg_type)
+static inline int to_reg(int gpio, enum ctrl_register reg_type)
 {
 	unsigned int reg;