valgrind: correct the comparison logic in vg_regtest

do_diffs in the vg_regtest script compares the actual test output
against the expected test output and returns 0 if it matches.

Previous upgrade modified the return value of do_diffs() and that
resulted in ptest failures.

[YOCTO #8471]

(From OE-Core rev: fa5f7b5090468da0ed1e30160e68362c97350c47)

Signed-off-by: Maxin B. John <maxin.john@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/valgrind/valgrind/0005-Modify-vg_test-wrapper-to-support-PTEST-formats.patch

@@ -100,7 +100,7 @@ index a441f42..cb05b52 100755
                  unlink("$name.$mid.out");
                  unlink(<$name.$mid.diff*>);
 -                return;
-+                return 1;
++                return 0;
              }
          }
      }
@@ -113,7 +113,7 @@ index a441f42..cb05b52 100755
         print "Failure encountered, stopping to loop\n";
         exit 1
      }
-+    return 0;
++    return 1;
  }
  
  sub do_one_test($$)