powerpc/64: ret_from_fork avoid restoring regs twice

If the system call return path always restores NVGPRs then there is no
need for ret_from_fork to do it. The HANDLER_RESTORE_NVGPRS does the
right thing for this.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230325122904.2375060-5-npiggin@gmail.com

arch/powerpc/kernel/interrupt_64.S

@@ -728,14 +728,14 @@ DEFINE_FIXED_SYMBOL(__end_soft_masked, text)
 #ifdef CONFIG_PPC_BOOK3S
 _GLOBAL(ret_from_fork_scv)
 	bl	schedule_tail
-	REST_NVGPRS(r1)
+	HANDLER_RESTORE_NVGPRS()
 	li	r3,0	/* fork() return value */
 	b	.Lsyscall_vectored_common_exit
 #endif
 
 _GLOBAL(ret_from_fork)
 	bl	schedule_tail
-	REST_NVGPRS(r1)
+	HANDLER_RESTORE_NVGPRS()
 	li	r3,0	/* fork() return value */
 	b	.Lsyscall_exit