msm: ipa: Fix to handle NULL pointer dereference

Header entry deleted but same entry pointer using in
routing table not updated. Added checks to confirm
header entry present or not before using it to avoid
null pointer dereference.

Change-Id: Id1d844c60b2dcb0cc7cf18352b78d62fe5a89347
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>