Silence the warning when building with -Wsign-compare when fb.h is
included:

include/linux/fb.h: In function ‘__fb_pad_aligned_buffer’:
include/linux/fb.h:650:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (j = 0; j < s_pitch; j++)
                 ^
Signed-off-by: NBrian W Hart <hartb@linux.vnet.ibm.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>