Kernel: Put USB request constants in namespace

Moved constants in USBRequest.h from global scope to the Kernel::USB
namespace.

Kernel/Bus/USB/USBRequest.h

@@ -9,6 +9,8 @@
 
 #include <AK/Types.h>
 
+namespace Kernel::USB {
+
 //
 // bmRequestType fields
 //
@@ -39,3 +41,5 @@ static constexpr u8 USB_REQUEST_GET_DESCRIPTOR = 0x06;
 static constexpr u8 USB_REQUEST_SET_DESCRIPTOR = 0x07;
 static constexpr u8 USB_REQUEST_GET_CONFIGURATION = 0x08;
 static constexpr u8 USB_REQUEST_SET_CONFIGURATION = 0x09;
+
+}