msm: ipa4: Fix to NULL pointer dereference

Accessing of the NULL pointer dereference causing the page fault issue.
Added check before accessing of NULL pointer to avoid NULL pointer
dereference.

Change-Id: I5e5bd6b418f305e785f3ec96af014494eebf1ffc
Acked-by: Ashok Vuyyuru <avuyyuru@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>