net: aquantia: remove function aq_ring_tx_deinit

Both functions aq_ring_rx_deinit() and aq_ring_tx_clean() are almost
identical aside from an additional check in the latter.
Move that check from the function into its caller and replace
aq_ring_rx_deinit() with aq_ring_rx_deinit().

By doing this also adjust the functions return value from int to void
since it can never fail.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Tested-by: Pavel Belous <pavel.belous@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>