V4L/DVB (11617): cx18: Set up to wait for a one-shot response before sending a firmware cmd

When sending an outgoing firmware command, prepare to wait before we raise the
interrupt, so we don't miss the wake_up() on the acknowledgment.  When waiting
for the acknowledgement, there is no need to loop around schedule(), as there
will only be one interrupt, and hence one wake_up(), issued.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>