linux-phytec-fsl

raid5-cache: correct condition for empty metadata write

As long as we recover one metadata block, we should write the empty metadata
write. The original code could make recovery corrupted if only one meta is
valid.

Reported-by: Zhengyuan Liu <liuzhengyuan@kylinos.cn>
Signed-off-by: Shaohua Li <shli@fb.com>