msm: ipa: fix compilation issue when IPA is disabled

Make change to define inline function when IPA is disabled.
Otherwise it will result in a compilation error.

Change-Id: I6979d15a6ed91aa0fb8be935a1646d77c4f82814
Acked-by: Chaitanya Pratapa <cpratapa@qti.qualcomm.com>
Signed-off-by: Ravinder Konka <rkonka@codeaurora.org>