dinput: Constify some variables

[Andrew Talbot]

Changelog:
    dinput: Constify some variables.

diff --git a/dlls/dinput/device_private.h b/dlls/dinput/device_private.h
index 43b28c9..fd5808d 100644
--- a/dlls/dinput/device_private.h
+++ b/dlls/dinput/device_private.h
@@ -94,7 +94,7 @@ typedef struct
     LONG lSaturation;
 } ObjProps;
 
-extern DWORD joystick_map_pov(POINTL *p);
+extern DWORD joystick_map_pov(const POINTL *p);
 extern LONG joystick_map_axis(ObjProps *props, int val);
 
 typedef struct
diff --git a/dlls/dinput/joystick.c b/dlls/dinput/joystick.c
index 0f39a6d..7d781c9 100644
--- a/dlls/dinput/joystick.c
+++ b/dlls/dinput/joystick.c
@@ -434,7 +434,7 @@ LONG joystick_map_axis(ObjProps *props, int val)
  *   22500   13500
  *       18000
  */
-DWORD joystick_map_pov(POINTL *p)
+DWORD joystick_map_pov(const POINTL *p)
 {
     if (p->x > 0)
         return p->y < 0 ?  4500 : !p->y ?  9000 : 13500;
diff --git a/dlls/dinput/joystick_private.h b/dlls/dinput/joystick_private.h
index aaa8294..0407e0a 100644
--- a/dlls/dinput/joystick_private.h
+++ b/dlls/dinput/joystick_private.h
@@ -55,7 +55,7 @@ typedef struct JoystickGenericImpl
 LONG joystick_map_axis(ObjProps *props, int val);
 HRESULT setup_dinput_options(JoystickGenericImpl *This, const int *default_axis_map);
 
-DWORD joystick_map_pov(POINTL *p);
+DWORD joystick_map_pov(const POINTL *p);
 
 HRESULT WINAPI JoystickWGenericImpl_GetObjectInfo(LPDIRECTINPUTDEVICE8W iface,
         LPDIDEVICEOBJECTINSTANCEW pdidoi, DWORD dwObj, DWORD dwHow);
diff --git a/dlls/dinput/mouse.c b/dlls/dinput/mouse.c
index e05d9e2..1599157 100644
--- a/dlls/dinput/mouse.c
+++ b/dlls/dinput/mouse.c
@@ -84,7 +84,7 @@ const GUID DInput_Wine_Mouse_GUID = { /* 9e573ed8-7734-11d2-8d4a-23903fb6bdf7 */
     0x9e573ed8, 0x7734, 0x11d2, {0x8d, 0x4a, 0x23, 0x90, 0x3f, 0xb6, 0xbd, 0xf7}
 };
 
-static void _dump_mouse_state(DIMOUSESTATE2 *m_state)
+static void _dump_mouse_state(const DIMOUSESTATE2 *m_state)
 {
     int i;