msm: bam_dmux: cleanup ioremap_nocache() handle during error handling

iounmap() needs to be called during error handling to cleanup the handle
returned by ioremap_nocache(), otherwise an unused hardware io to virtual
memory mapping will remain for the duration of system execution.

Change-Id: Ib568df713dcb3e4ec254df4bf76213c895554dd1
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>