net/mlx5: devlink health: use retained error fmsg API

Drop unneeded error checking.

devlink_fmsg_*() family of functions is now retaining errors,
so there is no need to check for them after each call.

Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>