media: dvb-frontends: mb86a16: remove useless variables in signal_det()

Remove useless variables wait_t and wait_sym and code related.

Also, fix some coding style issues.

Addresses-Coverity-ID: 1226947

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>