clk: actions: Add missing REGMAP_MMIO dependency

Add REGMAP_MMIO as dependency to avoid undefined
reference to regmap symbols.

Fixes: d85d2005 ("clk: actions: Add S900 SoC clock support")
Signed-off-by: Saravanan Sekar <sravanhome@gmail.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>