clk: imx: fix pll clock parents

pllx_bypass_src mux shouldn't be the parent of pllx clock
since it's only valid when when pllx BYPASS bit is set.
Thus it is actually one parent of pllx_bypass only.

Instead, pllx parent should be fixed to osc according to
reference manual.
Other plls have the same issue.

e.g. before fix, the pll tree is:
osc                                      6            6    24000000          0 0
   pll1_bypass_src                       0            0    24000000          0 0
      pll1                               0            0   792000000          0 0
         pll1_bypass                     0            0   792000000          0 0
            pll1_sys                     0            0   792000000          0 0

After the fix, it's:
osc                                      6            6    24000000          0 0
   pll1                                  0            0   792000000          0 0
      pll1_bypass                        0            0   792000000          0 0
         pll1_sys                        0            0   792000000          0 0

Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>