media: omap2: omapfb: fix boolreturn.cocci warnings

drivers/video/fbdev/omap2/omapfb/omapfb-main.c:290:9-10: WARNING: return of 0/1 in function 'cmp_var_to_colormode' with return type bool

 Return statements in functions returning bool should use
 true/false instead of 1/0.
Generated by: scripts/coccinelle/misc/boolreturn.cocci

Signed-off-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>