Cleanup: use mutex_lock() wrapper in rculfhash

Fixes this coverity issue:

*** CID 1375952:  Error handling issues  (CHECKED_RETURN)
/src/rculfhash.c: 1950 in cds_lfht_resize()
1944     }
1945
1946     void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size)
1947     {
1948             resize_target_update_count(ht, new_size);
1949             CMM_STORE_SHARED(ht->resize_initiated, 1);
>>>     CID 1375952:  Error handling issues  (CHECKED_RETURN)
>>>     Calling "pthread_mutex_lock" without checking return value (as is done elsewhere 44 out of 50 times).
1950             pthread_mutex_lock(&ht->resize_mutex);
1951             _do_cds_lfht_resize(ht);
1952             pthread_mutex_unlock(&ht->resize_mutex);
1953     }
1954
1955     static

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>