video: imxfb: fix imxfb_info configuration order

The devtype field for fbi (struct imxfb_info) must be set after memset call to
avoid some wrong behaviour (pixel size).

Signed-off-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@armadeus.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>