timeconst.pl: Eliminate Perl warning

defined(@array) is deprecated in Perl and gives off a warning.
Restructure the code to remove that warning.

[ hpa: it would be interesting to revert to the timeconst.bc script.
  It appears that the failures reported by akpm during testing of
  that script was due to a known broken version of make, not a problem
  with bc.  The Makefile rules could probably be restructured to avoid
  the make bug, or it is probably old enough that it doesn't matter. ]

Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org>

kernel/timeconst.pl

@@ -369,10 +369,8 @@ (@)
 		die "Usage: $0 HZ\n";
 	}
 
-	@val = @{$canned_values{$hz}};
-	if (!defined(@val)) {
-		@val = compute_values($hz);
-	}
+	$cv = $canned_values{$hz};
+	@val = defined($cv) ? @$cv : compute_values($hz);
 	output($hz, @val);
 }
 exit 0;