[#39] ir: Use defer for wg.Done()

Not important, but `exitOnErr` can alter control flow, let's be
explicit.

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

cmd/frostfs-ir/httpcomponent.go

@@ -50,8 +50,8 @@ func (c *httpComponent) start() {
 		log.Info(fmt.Sprintf("start %s", c.name))
 		wg.Add(1)
 		go func() {
+			defer wg.Done()
 			exitErr(c.srv.Serve())
-			wg.Done()
 		}()
 	}
 }