msm: ecm_ipa: Fix dereferencing a pointer before a NULL check

Inside ecm_ipa_tx_complete_notify() function there is
a dereference to pointer and then a NULL check.
NULL check needs to be done first to prevent NULL
pointer dereference.

Change-Id: If9a17a363898bafad73ee315a8be00fe76aa700a
Signed-off-by: Ghanim Fodi <gfodi@codeaurora.org>