msm: ipa: fix unclocked IPA register access

Due to interrupt mitigation logic, IPA driver can access IPA
BAM registers after IPA clocks have been turned off. This
commit ensures IPA remains clocked till polling operation is
completed.

Change-Id: I7c2175f9f1c1fae02c1bbaffde92941ddfc66ea9
Signed-off-by: Ravi Gummadidala <rgummadi@codeaurora.org>