media: imx: Don't initialize vars that won't be used

As reported by gcc:

  + drivers/staging/media/imx/imx-media-csi.c: warning: variable 'input_fi' set but not used [-Wunused-but-set-variable]:  => 671:33
  + drivers/staging/media/imx/imx-media-csi.c: warning: variable 'pinctrl' set but not used [-Wunused-but-set-variable]:  => 1742:18

input_fi is not used, so just remove it.

However, pinctrl should be used, as it devm_pinctrl_get_select_default()
is declared with attribute warn_unused_result. What's missing there
is an error handling code, in case it fails. Add it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>