vfs: allow O_PATH file descriptors for fstatfs()

Olga reported that file descriptors opened with O_PATH do not work with
fstatfs(), found during further development of ksh93's thread support.

There is no reason to not allow O_PATH file descriptors here (fstatfs is
very much a path operation), so use "fdget_raw()".  See commit
55815f7014 ("vfs: make O_PATH file descriptors usable for 'fstat()'")
for a very similar issue reported for fstat() by the same team.

Reported-and-tested-by: ольга крыжановская <olga.kryzhanovska@gmail.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org	# O_PATH introduced in 3.0+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/statfs.c

@@ -94,7 +94,7 @@ retry:
 
 int fd_statfs(int fd, struct kstatfs *st)
 {
-	struct fd f = fdget(fd);
+	struct fd f = fdget_raw(fd);
 	int error = -EBADF;
 	if (f.file) {
 		error = vfs_statfs(&f.file->f_path, st);