clk: imx7d: remove CLK_IS_CRITICAL flag for arm_a7_root_clk

clk: imx7d: remove CLK_IS_CRITICAL flag for arm_a7_root_clk

i.MX7D uses virtual cpu clock of "arm" clock to be child clock
of "arm_a7_root_clk" and it is with CLK_IS_CRITICAL flag set, so
no need to add CLK_IS_CRITICAL flag for keeping "arm_a7_root_clk"
use count correct, latest clock tree is as below in clk_summary:

pll_arm_main                         1        1        0   792000000          0
      pll_arm_main_bypass            1        1        0   792000000          0
         pll_arm_main_clk            1        1        0   792000000          0
            arm_a7_src               1        1        0   792000000          0
               arm_a7_cg             1        1        0   792000000          0
                  arm_a7_div         1        1        0   792000000          0
                     arm_a7_root_clk       1        1        0   792000000    0
                        arm          1        1        0   792000000

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>