mlxsw: Remove obsolete dependency on THERMAL=m

mlxsw: Remove obsolete dependency on THERMAL=m

The THERMAL configuration option was changed from tristate to bool, but
a dependency on THERMAL=m was forgotten, leading to a warning when
running "make savedefconfig":

    boolean symbol THERMAL tested for 'm'? test forced to 'n'

Fixes: be33e4fbbea581ea ("thermal/drivers/core: Remove the module Kconfig's option")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>