V4L/DVB (8532): mxl5007t: remove excessive locks

The use of mutex locking is overly paranoid in this driver.
The only locks we need are around the manipulation of the
register arrays. The other locks are not needed - remove them.

Thanks to Steven Toth for pointing this out.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>