net: renesas: rswitch: Fix unmasking irq condition

Fix unmasking irq condition by using napi_complete_done(). Otherwise,
redundant interrupts happen.

Fixes: 3590918b

 ("net: ethernet: renesas: Add support for "Ethernet Switch"")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>