OvmfPkg/ResetSystemLib: improve coding style in ResetSystem()

The cases under ResetSystem() currently mix "break"s with "return"s for no
good reason. Use "break" consistently.

(The inconsistency was introduced in commit 84c0b80de7,
"OvmfPkg/ResetSystemLib: Add new API ResetSystem", 2019-04-28.)

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Rebecca Cran <rebecca@bsdio.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2675
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200417153751.7110-4-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Rebecca Cran <rebecca@bsdio.com>

OvmfPkg/Library/ResetSystemLib/ResetSystemLib.c

@@ -157,13 +157,13 @@ ResetSystem (
 
   case EfiResetShutdown:
     ResetShutdown ();
-    return;
+    break;
 
   case EfiResetPlatformSpecific:
     ResetPlatformSpecific (DataSize, ResetData);
-    return;
+    break;
 
   default:
-    return;
+    break;
   }
 }