omap1: Fix compile for omap1_bl.c

Commit 9905a43b

 made struct backlight_ops const. Omap was
setting check_fb dynamically, which caused the following
compile error:

drivers/video/backlight/omap1_bl.c: In function 'omapbl_probe':
drivers/video/backlight/omap1_bl.c:142: error: assignment of read-only variable 'omapbl_ops'

Turns out pdata->check_fb is not being used, so just remove
it to fix the compile.

Cc: Emese Revfy <re.emese@gmail.com>
Cc: Richard Purdie <rpurdie@linux.intel.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>