msm: ipa: fix to use valid ep index value

When disabling agregation on Q6 pipes during SSR
there is a possibility that index -1 is used. Make
a change to skip processing if ep index is not valid.

Change-Id: I7578e582d1eda0b181225af9d00ec8ad5fbe372d
Acked-by: Chaitanya Pratapa <cpratapa@qti.qualcomm.com>
Signed-off-by: Ravinder Konka <rkonka@codeaurora.org>