drivers/gpio/max730x.c: add license macro

drivers/gpio/max730x.c: add license macro

According to the header in max730x it is licensed GPLv2.

Add a MODULE_LICENSE to avoid getting the kernel tainted.

[w.sang@pengutronix.de: add MODULE_AUTHOR and MODULE_DESCRIPTION also]
Signed-off-by: Richard Röjfors <richard.rojfors@pelagicore.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>