drm/nouveau/clk/gk20a: fix VCO bit mask

Fix the mask specified to switch to VCO mode was given as an (incorrect)
immediate value. Although the side-effect happens to be the same, this
is clearly incorrect.
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c

@@ -422,7 +422,8 @@ _gk20a_pllg_program_mnp(struct gk20a_clk *clk, bool allow_slide)
 		return -ETIMEDOUT;
 
 	/* switch to VCO mode */
-	nvkm_mask(device, SEL_VCO, 0, BIT(SEL_VCO_GPC2CLK_OUT_SHIFT));
+	nvkm_mask(device, SEL_VCO, BIT(SEL_VCO_GPC2CLK_OUT_SHIFT),
+		  BIT(SEL_VCO_GPC2CLK_OUT_SHIFT));
 
 	/* restore out divider 1:1 */
 	val = nvkm_rd32(device, GPC2CLK_OUT);