iio: inv_mpu6050: Clear timestamps fifo while resetting hardware fifo

commit 4dac0a8eefd55bb1f157d1a5a084531334a2d74c upstream.

A hardware fifo reset always imply an invalidation of the
existing timestamps, so we'll clear timestamps fifo on
successfull hardware fifo reset.

Signed-off-by: Viorel Suman <viorel.suman@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>