winecfg: fix a compiler warning on PowerPC

[Austin English]

char defaults to unsigned char on PowerPC, so new == -1 obviously fails.

-- 
-Austin
-------------- next part --------------
diff --git a/programs/winecfg/driveui.c b/programs/winecfg/driveui.c
index 87af06c..671d65f 100644
--- a/programs/winecfg/driveui.c
+++ b/programs/winecfg/driveui.c
@@ -340,7 +340,7 @@ static void on_add_click(HWND dialog)
        the default. In future we should be able to temporarily map /
        then invoke the directory chooser dialog. */
 
-    char new = 'C'; /* we skip A and B, they are historically floppy drives */
+    signed char new = 'C'; /* we skip A and B, they are historically floppy drives */
     ULONG mask = ~drive_available_mask(0); /* the mask is now which drives aren't available */
     int i, c;