iio: imu: inv_mpu6050: Fix code indent for if statement

This fixes the following checkpatch.pl warning:

WARNING: suspect code indent for conditional statements (8, 24)
+       if (kfifo_len(&st->timestamps) >
[...]
+                       goto flush_fifo;
Signed-off-by: NDaniel Baluta <daniel.baluta@intel.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>