cmd/objdump: defer closing the file after opening

Remove the os.Exit(0) to honor the deferred closing of the file.

Change-Id: Iaa9304d8203c8fec0ec728af669a94eadd36905c
Reviewed-on: https://go-review.googlesource.com/118915Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/objdump/main.go

@@ -75,6 +75,7 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
+	defer f.Close()
 
 	dis, err := f.Disasm()
 	if err != nil {
@@ -87,7 +88,6 @@ func main() {
 	case 1:
 		// disassembly of entire object
 		dis.Print(os.Stdout, symRE, 0, ^uint64(0), *printCode)
-		os.Exit(0)
 
 	case 3:
 		// disassembly of PC range
@@ -100,6 +100,5 @@ func main() {
 			log.Fatalf("invalid end PC: %v", err)
 		}
 		dis.Print(os.Stdout, symRE, start, end, *printCode)
-		os.Exit(0)
 	}
 }