misc: isa1200: Change mutex for isa1200 vibrator

Change i2c client device mutex to local driver mutex
for isa1200 vibrator which is used while enabling and
disabling the clock.

Change-Id: I4f61c629c503c658410b5c14da2e1612b82ec201
CRs-Fixed: 545512
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>