soc: qcom: bam_dmux: Use phys_addr_t for a2_phys_base

The phys_addr_t type exists to represent physical addresses.  a2_phys_base
is the physical address of the A2 BAM, but is incorrectly typed as a
void *.

Correctly represent a2_phys_base with the phys_addr_t type.

Change-Id: Iabf87a5099e8ec115afa4256c57037fb88a8fe97
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>