powerpc: copy_thread make ret_from_fork register setup consistent

The ret_from_fork code for 64e and 32-bit set r3 for
syscall_exit_prepare the same way that 64s does, so there should
be no need to special-case them in copy_thread.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-3-npiggin@gmail.com

arch/powerpc/kernel/entry_32.S

@@ -183,7 +183,7 @@ syscall_exit_finish:
 ret_from_fork:
 	REST_NVGPRS(r1)
 	bl	schedule_tail
-	li	r3,0
+	li	r3,0	/* fork() return value */
 	b	ret_from_syscall
 
 	.globl	ret_from_kernel_thread

arch/powerpc/kernel/process.c

@@ -1784,9 +1784,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 			childregs->gpr[1] = usp;
 		((unsigned long *)sp)[0] = childregs->gpr[1];
 		p->thread.regs = childregs;
-		/* 64s sets this in ret_from_fork */
-		if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64))
-			childregs->gpr[3] = 0;  /* Result from fork() */
 		if (clone_flags & CLONE_SETTLS) {
 			if (!is_32bit_task())
 				childregs->gpr[13] = tls;