btrfs: don't clobber ret in btrfs_validate_super()

In the Linux kernel, the following vulnerability has been resolved: btrfs: don't clobber ret in btrfs_validate_super() Commit 2a9bb78cfd36 ("btrfs: validate system chunk array at btrfs_validate_super()") introduces a call to validate_sys_chunk_array() in btrfs_validate_super(), which clobbers the value of ret set earlier. This has the effect of negating the validity checks done earlier, making it so btrfs could potentially try to mount invalid filesystems.