nir/libclc: handle null callee name when lowering

fixes a crash in the CTS spirv_new get_program_il test

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12230>

src/compiler/spirv/nir_lower_libclc.c

@@ -38,6 +38,10 @@ lower_clc_call_instr(nir_instr *instr, nir_builder *b,
 {
    nir_call_instr *call = nir_instr_as_call(instr);
    nir_function *func = NULL;
+
+   if (!call->callee->name)
+      return false;
+
    nir_foreach_function(function, clc_shader) {
       if (strcmp(function->name, call->callee->name) == 0) {
          func = function;