msm: camera: isp: Reset process_bubble during stop

If process_bubble is set and stop dev is called before resetting
process_bubble, then process_bubble is left set in isp_ctx. It results
in apply fail in upcoming sessions.

Change-Id: I2c542d61a0e42f6a89e26c74b67a1673b89f066d
Signed-off-by: Trishansh Bhardwaj <tbhardwa@codeaurora.org>