fbdev: sh_mobile_lcdc: Remove sh_mobile_lcdc_set_bpp()

The function duplicates code found in sh_mobile_check_var(). Remove
sh_mobile_lcdc_set_bpp() and call sh_mobile_check_var() instead.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>