block/rnbd-clt: Improve find_or_create_sess() return check

clang static analysis reports this problem

rnbd-clt.c:1212:11: warning: Branch condition evaluates to a
  garbage value
        else if (!first)
                 ^~~~~~

This is triggered in the find_and_get_or_create_sess() call
because the variable first is not initialized and the
earlier check is specifically for

	if (sess == ERR_PTR(-ENOMEM))

This is false positive.

But the if-check can be reduced by initializing first to
false and then returning if the call to find_or_creat_sess()
does not set it to true.  When it remains false, either
sess will be valid or not.  The not case is caught by
find_and_get_or_create_sess()'s caller rnbd_clt_map_device()

	sess = find_and_get_or_create_sess(...);
	if (IS_ERR(sess))
		return ERR_CAST(sess);

Since find_and_get_or_create_sess() initializes first to false
setting it in find_or_create_sess() is not needed.

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Link: https://lore.kernel.org/r/20210419073722.15351-12-gi-oh.kim@ionos.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-clt.c

@@ -910,6 +910,7 @@ again:
 	return NULL;
 }
 
+/* caller is responsible for initializing 'first' to false */
 static struct
 rnbd_clt_session *find_or_create_sess(const char *sessname, bool *first)
 {
@@ -925,8 +926,7 @@ rnbd_clt_session *find_or_create_sess(const char *sessname, bool *first)
 		}
 		list_add(&sess->list, &sess_list);
 		*first = true;
-	} else
-		*first = false;
+	}
 	mutex_unlock(&sess_lock);
 
 	return sess;
@@ -1194,13 +1194,11 @@ find_and_get_or_create_sess(const char *sessname,
 	struct rnbd_clt_session *sess;
 	struct rtrs_attrs attrs;
 	int err;
-	bool first;
+	bool first = false;
 	struct rtrs_clt_ops rtrs_ops;
 
 	sess = find_or_create_sess(sessname, &first);
-	if (sess == ERR_PTR(-ENOMEM))
-		return ERR_PTR(-ENOMEM);
-	else if (!first)
+	if (!first)
 		return sess;
 
 	if (!path_cnt) {