fbdev: savage: Handle err return when savagefb_check_var failed

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.

Fixes: 04e5eac8f3ab ("fbdev: savage: Error out if pixclock equals zero")
Signed-off-by: Cai Xinchen <caixinchen1@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Helge Deller <deller@gmx.de>