V4L/DVB (5699): Cinergyt2: fix file release handler

If this mutex_lock_interruptible() does fail due to signal_pending() then the
state of the driver will get trashed in interesting ways, because userspace
cannot and will not retry the close().

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>