video: fbdev: cobalt_lcdfb: Handle return NULL error from devm_ioremap

[ Upstream commit 4dcd19bfabaee8f9f4bcf203afba09b98ccbaf76 ]

Here, If devm_ioremap will fail. It will return NULL.
Kernel can run into a NULL-pointer dereference.
This error check will avoid NULL pointer dereference.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Acked-by: Yoichi Yuasa <yuasa@linux-mips.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>