mlxsw: reg: Increase register field length to 31 bits

The cited commit set a value of 2^31-1 in order to "disable" the shaper
on a given a port. However, the length of the maximum shaper rate field
was not updated from 28 bits to 31 bits, which means ports are still
limited to ~268Gbps despite supporting speeds of 400Gbps.

Fix this by increasing the field's length.

Fixes: 92afbfed

 ("mlxsw: reg: Increase MLXSW_REG_QEEC_MAS_DIS")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>