bnxt_en: Add page_pool_destroy() during RX ring cleanup.

Add page_pool_destroy() in bnxt_free_rx_rings() during normal RX ring
cleanup, as Ilias has informed us that the following commit has been
merged:

1da4bbef ("net: core: page_pool: add user refcnt and reintroduce page_pool_destroy")

The special error handling code to call page_pool_free() can now be
removed.  bnxt_free_rx_rings() will always be called during normal
shutdown or any error paths.

Fixes: 322b87ca

 ("bnxt_en: add page_pool support")
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Acked-by: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>