mlxsw: reg: Drop unnecessary writes from mlxsw_reg_sfmr_pack()

The MLXSW_REG_ZERO at the beginning of the function wipes the whole
payload. There's no need to set vtfp and vv to false explicitly.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/04a51ea7cf31eea0ef7707311d8e864e2d9ef307.1700503644.git.petrm@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>