iio: adis16475: fix deadlock on frequency set

With commit 39c024b51b
("iio: adis16475: improve sync scale mode handling"), two deadlocks were
introduced:
 1) The call to 'adis_write_reg_16()' was not changed to it's unlocked
    version.
 2) The lock was not being released on the success path of the function.

This change fixes both these issues.

Fixes: 39c024b51b ("iio: adis16475: improve sync scale mode handling")
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210920090047.74903-1-nuno.sa@analog.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/adis16475.c

@@ -353,10 +353,11 @@ static int adis16475_set_freq(struct adis16475 *st, const u32 freq)
 	if (dec > st->info->max_dec)
 		dec = st->info->max_dec;
 
-	ret = adis_write_reg_16(&st->adis, ADIS16475_REG_DEC_RATE, dec);
+	ret = __adis_write_reg_16(&st->adis, ADIS16475_REG_DEC_RATE, dec);
 	if (ret)
 		goto error;
 
+	adis_dev_unlock(&st->adis);
 	/*
 	 * If decimation is used, then gyro and accel data will have meaningful
 	 * bits on the LSB registers. This info is used on the trigger handler.