net: ipa: drop an unneeded transaction reference

In gsi_channel_update(), a reference count is taken on the last
completed transaction "to keep it from completing" before we give
the event back to the hardware.  Completion processing for that
transaction (and any other "new" ones) will not occur until after
this function returns, so there's no risk it completing early.  So
there's no need to take and drop the additional transaction
reference.

Use local variables in the call to gsi_evt_ring_doorbell().

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>