sw64: optimize instruction usage in fork routine

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5PNDF

--------------------------------

Use 'call' instead of 'jmp' in ret_from_fork(), so the 'ret' in
schedule_tail() won't mess up branch prediction.
Signed-off-by: NMao Minkai <maominkai@wxiat.com>
Signed-off-by: NGu Zitao <guzitao@wxiat.com>

arch/sw_64/kernel/entry.S

@@ -426,7 +426,7 @@ __switch_to:
 	.ent ret_from_fork
 ret_from_fork:
 	ldi	$26, ret_from_sys_call
-	jmp	$31, schedule_tail
+	call	$31, schedule_tail
 	.end ret_from_fork
 
 /*