clk: imx: fix i.MX7D peripheral clk mux flags

According to RM, Page 574, Chapter 5.2.6.4.3 Peripheral clock slice,
"IP clock slices must be stopped to change the clock source.".

So we must have CLK_SET_PARENT_GATE flag to avoid glitch.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>