clk: rockchip: initialize flags of clk_init_data in mmc-phase clock

The flags element of clk_init_data was never initialized for mmc-
phase-clocks resulting in the element containing a random value
and thus possibly enabling unwanted clock flags.

Fixes: 89bf26cb ("clk: rockchip: Add support for the mmc clock phases using the framework")
Cc: stable@vger.kernel.org
Signed-off-by: Heiko Stuebner <heiko@sntech.de>