selftests: ocelot: tc_flower_chains: streamline test output

Bring this driver-specific selftest output in line with the other
selftests.

Before:

Testing VLAN pop..                      OK
Testing VLAN push..                     OK
Testing ingress VLAN modification..             OK
Testing egress VLAN modification..              OK
Testing frame prioritization..          OK

After:

TEST: VLAN pop                                                      [ OK ]
TEST: VLAN push                                                     [ OK ]
TEST: Ingress VLAN modification                                     [ OK ]
TEST: Egress VLAN modification                                      [ OK ]
TEST: Frame prioritization                                          [ OK ]

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>