fbdev: stifb: Fix info entry in sti_struct on error path

[ Upstream commit 0bdf1ad8d10bd4e50a8b1a2c53d15984165f7fea ]

Minor fix to reset the info field to NULL in case of error.

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>