dccp: Fix compile warning in probe code.

dccp: Fix compile warning in probe code.

commit d984e6197ecd2babc1537f42dc1e676133005cda upstream.

Commit 1386be55e32a3c5d8ef4a2b243c530a7b664c02c ("dccp: fix
auto-loading of dccp(_probe)") fixed a bug but created a new
compiler warning:

net/dccp/probe.c: In function ‘dccpprobe_init’:
net/dccp/probe.c:166:2: warning: the omitted middle operand in ?: will always be ‘true’, suggest explicit middle operand [-Wparentheses]

try_then_request_module() is built for situations where the
"existence" test is some lookup function that returns a non-NULL
object on success, and with a reference count of some kind held.

Here we're looking for a success return of zero from the jprobe
registry.

Instead of fighting the way try_then_request_module() works, simply
open code what we want to happen in a local helper function.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>