nir: Fix anonymous union initialization with older GCC.

nir: Fix anonymous union initialization with older GCC.

Fix this build error with GCC 4.4.7.

  CC     nir/nir_opt_copy_prop_vars.lo
nir/nir_opt_copy_prop_vars.c: In function ‘load_element_from_ssa_entry_value’:
nir/nir_opt_copy_prop_vars.c:454: error: unknown field ‘ssa’ specified in initializer
nir/nir_opt_copy_prop_vars.c:455: error: unknown field ‘def’ specified in initializer
nir/nir_opt_copy_prop_vars.c:456: error: unknown field ‘component’ specified in initializer
nir/nir_opt_copy_prop_vars.c:456: error: extra brace group at end of initializer
nir/nir_opt_copy_prop_vars.c:456: error: (near initialization for ‘(anonymous).<anonymous>’)
nir/nir_opt_copy_prop_vars.c:456: warning: excess elements in union initializer
nir/nir_opt_copy_prop_vars.c:456: warning: (near initialization for ‘(anonymous).<anonymous>’)

Fixes: 96c32d77763c ("nir/copy_prop_vars: handle load/store of vector elements")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109810
Reviewed-by: Andres Gomez <agomez@igalia.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>