soc: qcom: bgcom: use kzalloc to allocate memory from common pool

Uses kzalloc for allocating the memory from common pool instead of
device memory pool to avoid bgcom thread starvation for memory
allocation.

Change-Id: I4ea45339bf649c62909bfd64f2d4eb80e728e118
Signed-off-by: Arjun Singh <arsingh@codeaurora.org>