mlxsw: pci: Fix missing error checking

I accidentally removed the error checking after issuing the reset.
Restore it.

Fixes: f257c73e ("mlxsw: pci: Add support for new reset flow")
Reported-by: Coverity Scan <scan-admin@coverity.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>