nds32: convert to setup_initial_init_mm()

Use setup_initial_init_mm() helper to simplify code.

Link: https://lkml.kernel.org/r/20210608083418.137226-9-wangkefeng.wang@huawei.comSigned-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Greentime Hu <green.hu@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/nds32/kernel/setup.c

@@ -294,10 +294,7 @@ void __init setup_arch(char **cmdline_p)
 
 	setup_cpuinfo();
 
-	init_mm.start_code = (unsigned long)&_stext;
-	init_mm.end_code = (unsigned long)&_etext;
-	init_mm.end_data = (unsigned long)&_edata;
-	init_mm.brk = (unsigned long)&_end;
+	setup_initial_init_mm(_stext, _etext, _edata, _end);
 
 	/* setup bootmem allocator */
 	setup_memory();