spl: dm: Kconfig: SPL_CLK depends on SPL_DM

SPL_CLK should also depend on SPL_DM (and not just on CLK).
Add the additional dependency.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>