media: rc: imon_raw: use fls rather than loop per bit

Previously, the code would loop for each of the 40 bits. Now it will
branch for each edge in the IR, which will be much less.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>