msm: bam_dmux: add handling for unsupported clocks

If any of the clocks bam_dmux normally uses is unsupported on a target,
bam_dmux should ignore that clock and proceed.

Change-Id: I6124059b23a3f6a4a6f3c3a7eeaaa1f9436de1b4
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>