fs/stat.c: remove unnecessary new_valid_dev() check

new_valid_dev() always returns 1, so the !new_valid_dev() check is not
needed.  Remove it.

Signed-off-by: Yaowei Bai <bywxiaobai@163.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>