net: ipa: pass GSI pointer to gsi_evt_ring_rx_update()

The only reason the event ring's channel pointer is needed in
gsi_evt_ring_rx_update() is so we can get at its GSI pointer.

We can pass the GSI pointer as an argument, along with the event
ring ID, and thereby avoid using the event ring channel pointer.
This is another step toward no longer assuming an event ring
services a single channel.

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