go: Update to latest keystone package API & Remove unnecessary else

- Currently can't building because not found const variables

- panic built-in function is always exist of program. Remove else and
  export 'ks' variable in the main function

Signed-off-by: Koichi Shiraishi <zchee.io@gmail.com>

bindings/go/keystone/samples/main.go

@@ -14,19 +14,19 @@ import (
 func main() {
 	assembly := os.Args[1]
 
-	if ks, err := keystone.New(keystone.ArchitectureX86, keystone.Mode32); err != nil {
+	ks, err := keystone.New(keystone.ARCH_X86, keystone.MODE_32)
+	if err != nil {
 		panic(err)
-	} else {
-		defer ks.Close()
+	}
+	defer ks.Close()
 
-		if err := ks.Option(keystone.OptionSyntax, keystone.OptionSyntaxIntel); err != nil {
-			panic(fmt.Errorf("Could not set syntax option to intel"))
-		}
+	if err := ks.Option(keystone.OPT_SYNTAX, keystone.OPT_SYNTAX_INTEL); err != nil {
+		panic(fmt.Errorf("Could not set syntax option to intel"))
+	}
 
-		if insn, _, ok := ks.Assemble(assembly, 0); !ok {
-			panic(fmt.Errorf("Could not assemble instruction"))
-		} else {
-			fmt.Printf("%s: [%x]", assembly, insn)
-		}
+	if insn, _, ok := ks.Assemble(assembly, 0); !ok {
+		panic(fmt.Errorf("Could not assemble instruction"))
+	} else {
+		fmt.Printf("%s: [%x]", assembly, insn)
 	}
 }