drivers/video/backlight/vgg2432a4.c: add missing const

Add 'const' to static array that was missing it in its definition.  Also,
'const' is added to ili9320_write_regs(), because it is called by
vgg2432a4 driver.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>