clk: imx: clk-sscg-pll: Drop unnecessary initialization

No need to initialize 'ret' in many functions, as it will get
the return value from function call, so remove the initializtion
of 'ret'.

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