media: em28xx: calculate left volume level correctly

The calculation of the left volume looks suspect, the value of
0x1f - ((val << 8) & 0x1f) is always 0x1f. The debug prior to the
assignment of value[1] prints the left volume setting using the
calculation 0x1f - (val >> 8) & 0x1f which looks correct to me.
Fix the left volume by using the correct expression as used in
the debug.

Detected by CoverityScan, CID#146140 ("Wrong operator used")

Fixes: 850d24a5 ("[media] em28xx-alsa: add mixer support for AC97 volume controls")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>