net/mlx5: E-switch, Return correct error code on group creation failure

Dan Carpenter report:
The patch f47e04eb: "net/mlx5: E-switch, Allow setting share/max
tx rate limits of rate groups" from May 31, 2021, leads to the
following Smatch static checker warning:

	drivers/net/ethernet/mellanox/mlx5/core/esw/qos.c:483 esw_qos_create_rate_group()
	warn: passing zero to 'ERR_PTR'

If min rate normalization failed then error code may be overwritten to 0
if scheduling element destruction succeed. Ignore this value and always
return initial one.

Fixes: f47e04eb

 ("net/mlx5: E-switch, Allow setting share/max tx rate limits of rate groups")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Dmytro Linkin <dlinkin@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>