fbdev: imsttfb: Release framebuffer and dealloc cmap on error path

[ Upstream commit 5cf9a090

 ]

Add missing cleanups in error path.

Signed-off-by: Helge Deller <deller@gmx.de>
Stable-dep-of: e08c30ef

 ("fbdev: imsttfb: fix double free in probe()")
Signed-off-by: Sasha Levin <sashal@kernel.org>