autofs4: remove unneeded null check in try_to_fill_dentry()

After 97e7449a

: "autofs4: fix indirect mount pending expire race" we no
longer assumed that "ino" can be null.  The other null checks got removed
but this was one was missed.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>