[media] Fix cx88 remote control input

In the IR interrupt handler of cx88-input.c there's a 32-bit multiply
overflow which causes IR pulse durations to be incorrectly calculated.

This is a regression caused by commit 2997137b.

Cc: stable@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>