net: Include appropriate header file in caif/cfsrvl.c

Include appropriate header file net/caif/caif_dev.h in caif/cfsrvl.c
because it has prototype declaration of functions defined in
caif/cfsrvl.c.

This eliminates the following warning in caif/cfsrvl.c:
net/caif/cfsrvl.c:198:6: warning: no previous prototype for ‘caif_free_client’ [-Wmissing-prototypes]
net/caif/cfsrvl.c:208:6: warning: no previous prototype for ‘caif_client_register_refcnt’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: David S. Miller <davem@davemloft.net>