Fix signed/unsigned comparison warnings.

diff --git a/dlls/dinput/dinput_main.c b/dlls/dinput/dinput_main.c
index c98bb3d..fdc9350 100644
--- a/dlls/dinput/dinput_main.c
+++ b/dlls/dinput/dinput_main.c
@@ -206,7 +206,7 @@
 
 static void _dump_EnumDevices_dwFlags(DWORD dwFlags) {
     if (TRACE_ON(dinput)) {
-	int   i;
+	unsigned int   i;
 	static const struct {
 	    DWORD       mask;
 	    const char  *name;