thermal: imx: save one condition block for normal case of nvmem initialization

Put return value checks of calling imx_init_from_nvmem_cells()
into one block to save one condition block for normal case.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>