fbdev: imxfb: Removed unneeded release_mem_region

Remove unnecessary release_mem_region from the error path to prevent
mem region from being released twice, which could avoid resource leak
or other unexpected issues.

Fixes: b083c22d ("video: fbdev: imxfb: Convert request_mem_region + ioremap to devm_ioremap_resource")
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Helge Deller <deller@gmx.de>