msm: camera: Unlock the VFE kernel driver while waiting

When VFE is streaming and when we try to stream on/off the
secondary stream, the driver waits until the settings gets
reflected before returning the call. This blocks any other requests
for this wait duration. Unblock the VFE driver while waiting
for the settings to get reflected.

Change-Id: I42a9d888a936d51c17ae5e97262ce5ef0010dd0b
Signed-off-by: Nagesh Subba Reddy <nageshsreddy@codeaurora.org>