Fix Sparse warning:

sound/usb/mixer_scarlett_gen2.c:1949:24: warning: cast to restricted
__le32
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200902212133.30964-13-pierre-louis.bossart@linux.intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>