block/curl: Fix wrong free statement

Report from smatch:
block/curl.c:546 curl_close(21) info: redundant null check on s->url calling free()

The check was redundant, and free was also wrong because the memory
was allocated using g_strdup.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/curl.c

@@ -542,8 +542,7 @@ static void curl_close(BlockDriverState *bs)
     }
     if (s->multi)
         curl_multi_cleanup(s->multi);
-    if (s->url)
-        free(s->url);
+    g_free(s->url);
 }
 
 static int64_t curl_getlength(BlockDriverState *bs)