drivers/gpio/pm8916_gpio.c: Make pid be uint32_t

If get_dev_addr fails it will return FDT_ADDR_T_NONE and:
>>>     "priv->pid == 4294967295U" is always false regardless of the values of its operands. This occurs as the logical operand of if.

Cc: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
Reported-by: Coverity (CID: 143913)
Signed-off-by: Tom Rini <trini@konsulko.com>