drivers: iio: imu: Fixed null pointer issue when early buffer disabled

Fixed NUL pointer issue with mutex lock when early buffer disabled
for sensor ASM330, IAM20680 and SMI130.

Change-Id: If750e60ee9c47d978458ec8ae46d7f0d0d386d75
Signed-off-by: Puneet Yatnal <puneet@codeaurora.org>
5 files changed