riscv: convert to setup_initial_init_mm()

Use setup_initial_init_mm() helper to simplify code.

Link: https://lkml.kernel.org/r/20210608083418.137226-13-wangkefeng.wang@huawei.comSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/riscv/kernel/setup.c

@@ -264,10 +264,7 @@ static void __init parse_dtb(void)
 void __init setup_arch(char **cmdline_p)
 {
 	parse_dtb();
-	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);
 
 	*cmdline_p = boot_command_line;