nfc: llcp: nullify llcp_sock->dev on connect() error paths

Nullify the llcp_sock->dev on llcp_sock_connect() error paths,
symmetrically to the code llcp_sock_bind().  The non-NULL value of
llcp_sock->dev is used in a few places to check whether the socket is
still valid.

There was no particular issue observed with missing NULL assignment in
connect() error path, however a similar case - in the bind() error path
- was triggereable.  That one was fixed in commit 4ac06a1e ("nfc:
fix NULL ptr dereference in llcp_sock_getname() after failed connect"),
so the change here seems logical as well.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>