Fix an inappropriate sscanf return value judgment

This fixes an inappropriate sscanf return value judgment that
res check here is not needed while res2 is the one that need to be checked

Test: mm -j 8
Change-Id: I3e332286c9434d5b9d01421f5f421039f84ad6c7

system/bta/hf_client/bta_hf_client_at.cc

@@ -1246,7 +1246,7 @@ static char* bta_hf_client_parse_clcc(tBTA_HF_CLIENT_CB* client_cb,
 
     if (res2 == 0) {
       res2 = sscanf(buffer, ",\"\",%hu%n", &type, &offset);
-      if (res < 0) return NULL;
+      if (res2 < 0) return NULL;
 
       /* numstr is not matched in second attempt, correct this */
       res2++;