msm: qdsp5v2: remove pmem_kfree

pmem_kfree is now replaced by free_contiguous_memory_by_paddr.
Migrate to that API directly since the call to pmem_kfree is
just free_contiguous_memory_by_paddr anyway.

Change-Id: I5138369e54396a9418862159ea1a29d4bd21b9e6
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>