[janitor] dlls/winmm/mciavi -Wwrite-strings cleanup

[MichaelGuennewig@gmx.de (Michael Günnewig)]

Fixed warnings with gcc option "-Wwrite-strings".

--- dlls/winmm/mciavi/wnd.c.~1.7.~	2003-09-10 09:09:56.000000000 +0200
+++ dlls/winmm/mciavi/wnd.c	2003-10-03 13:45:12.000000000 +0200
@@ -164,7 +164,7 @@
 DWORD	MCIAVI_mciWhere(UINT wDevID, DWORD dwFlags, LPMCI_DGV_RECT_PARMS lpParms)
 {
     WINE_MCIAVI*	wma = MCIAVI_mciGetOpenDev(wDevID);
-    LPSTR		x = "";
+    LPCSTR		x = "";
 
     TRACE("(%04x, %08lx, %p)\n", wDevID, dwFlags, lpParms);