fbdev: savage: Handle err return when savagefb_check_var failed

In the Linux kernel, the following vulnerability has been resolved: fbdev: savage: Handle err return when savagefb_check_var failed The commit 04e5eac8f3ab("fbdev: savage: Error out if pixclock equals zero") checks the value of pixclock to avoid divide-by-zero error. However the function savagefb_probe doesn't handle the error return of savagefb_check_var. When pixclock is 0, it will cause divide-by-zero error.