Fix possible undefined value in check-symsorting.pl

It is possible for $line to be undefined at first used, if
the symfile doesn't have a section prefix (which is the case
for auto-generated symfiles).
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/check-symsorting.pl

@@ -11,7 +11,7 @@ my $lastgroup = undef;
 foreach my $symfile (@ARGV) {
     open SYMFILE, $symfile or die "cannot read $symfile: $!";
 
-    my $line;
+    my $line = 0;
     my $groupfile = "";
     my @group;