gpio: using common order: let 'static const' instead of 'const static'

  'const static ' is not a common order, better to use 'static const' instead.

building:
  make EXTRA_CFLAGS=-W ARCH=arm

  drivers/gpio/gpio-omap.c:1479:
    warning: 'static' is not at beginning of declaration
  drivers/gpio/gpio-omap.c:1485:
    warning: 'static' is not at beginning of declaration
  drivers/gpio/gpio-omap.c:1491:
    warning: 'static' is not at beginning of declaration

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>