ASoC: soc-core: Fix integer overflow

Integer overflow observed in the function to get the values of
mixer controls. Update type of mask from int to unsigned int
and do explicit type casting to fix the issue.

CRs-Fixed: 981735
Change-Id: I8fd40aa75b2d79f116df6b5e7508548f0c938343
Signed-off-by: Venkata Narendra Kumar Gutta <vgutta@codeaurora.org>