ads2gas: Use the correct perl string comparison operator

Using == ended up matching no matter what string was passed in
(which so far only happened if when the -thumb parameter
was set).

Change-Id: Ifa7b611d016d984aec3b697b5a1a07839f7508dc

build/make/ads2gas.pl

@@ -21,7 +21,7 @@
 my $thumb = 0;
 
 foreach my $arg (@ARGV) {
-    $thumb = 1 if ($arg == "-thumb");
+    $thumb = 1 if ($arg eq "-thumb");
 }
 
 print "@ This file was created from a .asm file\n";