firmware: remove unused __fw_state_is_done()

After commit e44565f6 ("firmware: fix batched requests - wake all waiters")
where we moved away from swait to old wait with a completion we also
stopped using __fw_state_is_done(). Since this is longer used kill it.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>