drm/nouveau: fix reclocking on nv40

In commit 77145f1c was introduced
error which cause that reclocking on nv40 not working anymore.
There is missing assigment of return value from pll_calc to ret.
Signed-off-by: NPali Rohár <pali.rohar@gmail.com>
Signed-off-by: NMartin Peres <martin.peres@labri.fr>
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv40_pm.c

@@ -131,7 +131,7 @@ nv40_calc_pll(struct drm_device *dev, u32 reg, struct nvbios_pll *pll,
 	if (clk < pll->vco1.max_freq)
 		pll->vco2.max_freq = 0;
 
-	pclk->pll_calc(pclk, pll, clk, &coef);
+	ret = pclk->pll_calc(pclk, pll, clk, &coef);
 	if (ret == 0)
 		return -ERANGE;