nir/validate: fix null deref coverity warning

CID 1265536 (#1 of 2): Explicit null dereferenced (FORWARD_NULL)6.
var_deref_op: Dereferencing null pointer parent.

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
1 file changed