ceph: remove unnecessary check for NULL in parse_longname()

Function ceph_get_inode() never returns NULL; instead it returns an
ERR_PTR() if something fails.  Thus, the check for NULL in parse_longname()
is useless and can be dropped.  Instead, move there the debug code that
does the error checking so that it's only executed if ceph_get_inode() is
called.

Fixes: dd66df00

 ("ceph: add support for encrypted snapshot names")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>