bnxt_en: Always set output parameters in bnxt_get_max_rings().

The current code returns -ENOMEM and does not bother to set the output
parameters to 0 when no rings are available.  Some callers, such as
bnxt_get_channels() will display garbage ring numbers when that happens.
Fix it by always setting the output parameters.

Fixes: 6e6c5a57 ("bnxt_en: Modify bnxt_get_max_rings() to support shared or non shared rings.")
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>