drm/nv50/clk: wire up pll_calc hook

Fixes crash during reclocking.
Call Trace:
 pll_calc == NULL
 calc_pll
 calc_mclk
 nv50_pm_clocks_pre
 nouveau_pm_perflvl_set
 nouveau_pm_trigger
 nouveau_pm_profile_set
 nouveau_pm_set_perflvl
 dev_attr_store
 sysfs_write_file
 vfs_write
 sys_write
 system_call_fastpath

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/subdev/clock/nv50.c

@@ -90,6 +90,7 @@ nv50_clock_ctor(struct nouveau_object *parent, struct nouveau_object *engine,
 		return ret;
 
 	priv->base.pll_set = nv50_clock_pll_set;
+	priv->base.pll_calc = nv04_clock_pll_calc;
 	return 0;
 }