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>