media: rc: validate that "rc_proto" is reasonable

Smatch complains that "rc_proto" comes from the user and it can result
in shift wrapping in ir_raw_encode_scancode()

    drivers/media/rc/rc-ir-raw.c:526 ir_raw_encode_scancode()
    error: undefined (user controlled) shift '1 << protocol'

This is true, but I reviewed the surrounding code and it appears
harmless. Anyway, let's verify that "rc_proto" is valid as a kernel
hardening measure.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>