gallium: reduce signed/unsigned warnings
diff --git a/src/gallium/auxiliary/draw/draw_passthrough.c b/src/gallium/auxiliary/draw/draw_passthrough.c
index fc2dde3..a51fa0a 100644
--- a/src/gallium/auxiliary/draw/draw_passthrough.c
+++ b/src/gallium/auxiliary/draw/draw_passthrough.c
@@ -78,7 +78,7 @@
 {
    const unsigned *pitch   = draw->vertex_fetch.pitch;
    const ubyte **src       = draw->vertex_fetch.src_ptr;
-   int i;
+   unsigned i;
 
    const ubyte *xyzw = src[0] + start * pitch[0];
    const ubyte *rgba = src[1] + start * pitch[1];