msm: ipa: fix a double clock disable for imp

Remove an incorrect clock disable from IPA MHI Proxy.

Change-Id: Id4f99822ce1453161d43bc79582d8b8f171d4539
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>