iio: imu: mpu6050: fix INV_MPU6050_REG_UP_TIME delay

replace msleep(INV_MPU6050_REG_UP_TIME) with usleep_range calls
due to fact the wait time is under 20 milliseconds.

Signed-off-by: Matt Ranostay <matt.ranostay@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>