fbdev: savage: Handle err return when savagefb_check_var failed

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UBUNTU-CVE-2024-26778

In the Linux kernel, the following vulnerability has been resolved: fbdev: savage: Error out if pixclock equals zero The userspace program could pass any values to the driver through ioctl interface. If the driver doesn't check the value of pixclock, it may cause divide-by-zero error. Although...