gpio: ep93xx: fix test for end of loop

The problem is that if port == ARRAY_SIZE() and "gc == &epg->gc[port]"
then that should be treated as invalid.

Fixes: fd935fc4 ("gpio: ep93xx: Do not pingpong irq numbers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>