We should be checking for IS_ERR() instead of NULL because
drm_dev_alloc() returns error pointers.

Fixes: 45d59d70 ("drm: Add new driver for MXSFB controller")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161213122332.GA7519@elgon.mountain

Add new driver for the MXSFB controller found in i.MX23/28/6SX .
The MXSFB controller is a simple framebuffer controller with one
parallel LCD output. Unlike the MXSFB fbdev driver that is used
on these systems now, this driver uses the DRM/KMS framework.
Signed-off-by: NMarek Vasut <marex@denx.de>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Shawn Guo <shawnguo@kernel.org>