Deobfuscate cleanup path in clnt_dg_create(..)

Similar to r300836 and r301800, cl and cu will always be non-NULL as they're
allocated using the mem_alloc routines, which always use
malloc(..., M_WAITOK).

Deobfuscating the cleanup path fixes a leak where if cl was NULL and
cu was not, cu would not be free'd, and also removes a duplicate test for
cl not being NULL.

MFC after: 1 week
Reported by: Coverity
CID: 1007033, 1007344
Sponsored by: EMC / Isilon Storage Division