gpio/omap: Fix section warning for omap_mpuio_alloc_gc()

Make omap_mpuio_alloc_gc() __devinit as omap_gpio_chip_init()
is __devinit. Otherwise we get:

WARNING: vmlinux.o(.devinit.text+0xa10): Section mismatch in reference
from the function omap_gpio_chip_init() to the function .init.text:omap_mpuio_alloc_gc()
The function __devinit omap_gpio_chip_init() references
a function __init omap_mpuio_alloc_gc().
If omap_mpuio_alloc_gc is only used by omap_gpio_chip_init then
annotate omap_mpuio_alloc_gc with a matching annotation.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>