driver: iio: imu: Fixed minor bugs of ASM330 sensor

Fixed NULL pointer dereference of sensor ASM330 in initalization
of early buffer feature and avoid writing to any syfs entry from
userspace while buffering sensor data because which leads
to buffer data loss.
Fixed the initial values of gyro is high in early buffer data
because sensor not initialized properly. Its expected to have
delay after each write and fix order of config as well.

Change-Id: I0f5ddc7b0b485c256ec1401f1ac83431c8f67493
Signed-off-by: Puneet Yatnal <puneet@codeaurora.org>