eCryptfs: Fix redundant error check on ecryptfs_find_daemon_by_euid()

It is sufficient to check the return code of
ecryptfs_find_daemon_by_euid(). If it returns 0, it always sets the
daemon pointer to point to a valid ecryptfs_daemon.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Reported-by: Kees Cook <keescook@chromium.org>