mlxsw: Fix naming convention of MFDE fields

Currently, the MFDE register field names are using the convention:
reg_mfde_<NAME_OF_FIELD>, and do not consider the name of the MFDE
event.

Fix the field names so they fit the more accurate convention:
reg_mfde_<NAME_OF_EVENT>_<NAME_OF_FIELD>.

Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>