Kernel: Let MouseDevice and KeyboardDevice write method return EINVAL

Currently, writing anything to `/dev/mouse0` or `/dev/keyboard0` causes
the Kernel to panic. The reason for this is that
`[Mouse,Keyboard]Device::write` always returns 0, which is explicitly
prohibited by `VERIFY` macro in `Process::sys$write`.  The fix seems
trivial; `write` should return EINVAL instead (as is the case with, for
example, `KCOVDevice`).

Kernel/Devices/HID/MouseDevice.cpp

@@ -48,9 +48,4 @@ KResultOr<size_t> MouseDevice::read(OpenFileDescription&, u64, UserOrKernelBuffe
     return nread;
 }
 
-KResultOr<size_t> MouseDevice::write(OpenFileDescription&, u64, const UserOrKernelBuffer&, size_t)
-{
-    return 0;
-}
-
 }