target: simplify transport_put_cmd

Inline two simple functions only used by it, and replace a goto
with a simple if else construct.

Note that the code moved from transport_dec_and_check seems fairly
buggy - the atomic_read check on a variable where we'd do an
atomic_dec_and_test looks racy if we'll ever get someone increment
it without the lock held around them (which it looks like we do),
and not decrementing the second counter if the first one doesn't
hit zero also at least needs an explanation.

(nab: Fix transport_put_cmd breakage)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>