net: ipa: skip some cleanup for unused transactions

In gsi_trans_free(), there's no point in ipa_gsi_trans_release() if
a transaction is unused.  No used TREs means no IPA layer resources
to clean up.  So only call ipa_gsi_trans_release() if at least one
TRE was used.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>