net: caif: add proper error handling

caif_enroll_dev() can fail in some cases. Ingnoring
these cases can lead to memory leak due to not assigning
link_support pointer to anywhere.

Fixes: 7c18d220

 ("caif: Restructure how link caif link layer enroll")
Cc: stable@vger.kernel.org
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>