video: hgafb: correctly handle card detect failure during probe

The return value of hga_card_detect() is not properly handled causing
the probe to succeed even though hga_card_detect() failed. Since probe
succeeds, hgafb_open() can be called which will end up operating on an
unmapped hga_vram. This results in an out-of-bounds access as reported
by kernel test robot [1].

To fix this, correctly detect failure of hga_card_detect() by checking
for a non-zero error code.

[1]: https://lore.kernel.org/lkml/20210516150019.GB25903@xsang-OptiPlex-9020/

Fixes: dc13cac ("video: hgafb: fix potential NULL pointer dereference")
Cc: stable <stable@vger.kernel.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Reviewed-by: Igor Matheus Andrade Torrente <igormtorrente@gmail.com>
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20210516192714.25823-1-mail@anirudhrb.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: anirudhrb

drivers/video/fbdev/hgafb.c

@@ -558,7 +558,7 @@ static int hgafb_probe(struct platform_device *pdev)
 	int ret;
 
 	ret = hga_card_detect();
-	if (!ret)
+	if (ret)
 		return ret;
 
 	printk(KERN_INFO "hgafb: %s with %ldK of memory detected.\n",