MLK-21296 clk: imx8mm: Remove CLK_SET_RATE_GATE from arm_a53_div

On recent kernels clks which are marked with CLK_SET_RATE_GATE are
"protected" against further changes at clk_prepare time. This
clk_core_rate_protect propagates up the clk tree and causes cpufreq
switches to fail later on.

See drivers/clk/clk.c around line 770.

Fix this by removing the CLK_SET_RATE_GATE flag for this specific clk.
This is safe because a53 clks are always only manipulated through
cpufreq.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Bai Ping <ping.bai@nxp.com>