audiodlkm: modify audiodlkm to parse amixer command correctly

0xFFFFFFFF will be parsed as -1.
But as the fourth parameter of SOC_SINGLE_MULTI_EXT(), it denotes 'xmax'
and should be larger than the sixth parameter.
0x7FFFFFFF works fine in this function.

Change-Id: Ie20437f5e1993dac337f52026343383a98db7f5e
Signed-off-by: Guodong Hu <guodhu@codeaurora.org>