mlxsw: reg: Rename MLXSW_REG_PPCNT_TC_CONG_TC to _CNT

The name does not make sense as it is. Clearly there is a typo and the
suffix should have been _CNT, like the other enumerators. Fix accordingly.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>