aty128fb: test below 0 on unsigned pll->post_divider

pll->post_divider is unsigned, so the test fails

Signed-off-by: Roel Kluin <12o3l@tiscali.nl>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/aty/aty128fb.c

@@ -1339,18 +1339,16 @@ static int aty128_var_to_pll(u32 period_in_ps, struct aty128_pll *pll,
 	if (vclk * 12 < c.ppll_min)
 		vclk = c.ppll_min/12;
 
-	pll->post_divider = -1;
-
 	/* now, find an acceptable divider */
-	for (i = 0; i < sizeof(post_dividers); i++) {
+	for (i = 0; i < ARRAY_SIZE(post_dividers); i++) {
 		output_freq = post_dividers[i] * vclk;
 		if (output_freq >= c.ppll_min && output_freq <= c.ppll_max) {
 			pll->post_divider = post_dividers[i];
 			break;
 		}
 	}
 
-	if (pll->post_divider < 0)
+	if (i == ARRAY_SIZE(post_dividers))
 		return -EINVAL;
 
 	/* calculate feedback divider */