Initialize HASHCTL differently, to suppress Coverity warning

Initialize HASHCTL differently, to suppress Coverity warning

Coverity complained that the hash_create() call might access
hash_table_ctl->hctl. That's a false alarm, hash_create() only
accesses that field when passed the HASH_SHARED_MEM flag. Try to
silence it by using a plain local variable instead of a const. That's
how the HASHCTL is initialized in all the other hash_create() calls.