softpipe: Silence compiler warnings on Windows.

src/gallium/drivers/softpipe/sp_tex_sample.c

@@ -601,9 +601,9 @@ get_texel(struct tgsi_sampler *sampler,
           unsigned face, unsigned level, int x, int y, int z,
           float rgba[NUM_CHANNELS][QUAD_SIZE], unsigned j)
 {
-   if (x < 0 || x >= sampler->texture->width[level] ||
-       y < 0 || y >= sampler->texture->height[level] ||
-       z < 0 || z >= sampler->texture->depth[level]) {
+   if (x < 0 || x >= (int) sampler->texture->width[level] ||
+       y < 0 || y >= (int) sampler->texture->height[level] ||
+       z < 0 || z >= (int) sampler->texture->depth[level]) {
       rgba[0][j] = sampler->state->border_color[0];
       rgba[1][j] = sampler->state->border_color[1];
       rgba[2][j] = sampler->state->border_color[2];