video: fbdev: sh_mobile_lcdcfb: constify sh_mobile_lcdc_bl_ops.

File size before:
text	data	 bss    dec      hex filename
 17525	 952	   0  18477	482d drivers/video/fbdev/sh_mobile_lcdcfb.o

File size After adding 'const':
text	data	 bss	 dec	 hex filename
 17557	 920	   0   18477	482d drivers/video/fbdev/sh_mobile_lcdcfb.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Cc: geert+renesas@glider.be
Cc: keescook@chromium.org
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>