As reported by smatch/sparse:

	drivers/media/i2c/ov7251.c:1381 ov7251_s_stream() warn: inconsistent returns '&ov7251->lock'.
	  Locked on  : 1381
	  Unlocked on: 1377

There's a lock unbalance at this routine, as it keeps the lock on
certain errors. Fix it.
Signed-off-by: NMauro Carvalho Chehab <mchehab@kernel.org>