net: ipa: simplify gsi_channel_trans_last()

Using a little logic we can simplify gsi_channel_trans_last().

The first condition in that function looks like this:
    if (trans_info->allocated_id != trans_info->free_id)
And if that's false, we proceed to the next one:
    if (trans_info->committed_id != trans_info->allocated_id)

Failure of the first test implies:
    trans_info->allocated_id == trans_info->free_id
And therefore, the second one can be rewritten this way:
    if (trans_info->committed_id != trans_info->free_id)

Substituting free_id for allocated_id and committed_id can also be
done in the code blocks executed when these conditions yield true.
The net result is that all three blocks for TX endpoints can be
consolidated into just one.

The two blocks of code at the end of that function (used for both TX
and RX channels) can be similarly consolidated into a single block.

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