drm/i915: Protect against leaks in pipe_crc_set_source

Stupid userspace (there is no evil userspace in debugfs by assumption)
might provoke a leak since we allocate the new array without holding
any locks. Drop in an unconditional kfree to deal with this - kfree
can handle NULL.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>