gpio: Use __devexit at necessary places

The function gen_74x164_remove and mc33880_remove are used only wrapped
by __devexit_p so define it using __devexit.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

diff --cc drivers/gpio/74x164.c
Simple merge

diff --cc drivers/gpio/mc33880.c
Simple merge