mlxsw: core: Add QSFP module temperature label attribute to hwmon

Add label attribute to hwmon object for exposing QSFP module's
temperature sensor name. Modules are labeled as "front panel xxx". The
label is used by utilities such as "sensors":

front panel 001:   +0.0C  (crit =  +0.0C, emerg =  +0.0C)
..
front panel 020:  +31.0C  (crit = +70.0C, emerg = +80.0C)
..
front panel 056:  +41.0C  (crit = +70.0C, emerg = +80.0C)

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>