sh64: kernel: use 'usp' instead of 'fn'

'fn' is not defined, according to the implementation copy_thread() in
'sh32', need use 'usp' instead of.
Signed-off-by: NChen Gang <gang.chen@asianux.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/sh/kernel/process_64.c

@@ -393,7 +393,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 	if (unlikely(p->flags & PF_KTHREAD)) {
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->regs[2] = (unsigned long)arg;
-		childregs->regs[3] = (unsigned long)fn;
+		childregs->regs[3] = (unsigned long)usp;
 		childregs->sr = (1 << 30); /* not user_mode */
 		childregs->sr |= SR_FD; /* Invalidate FPU flag */
 		p->thread.pc = (unsigned long) ret_from_kernel_thread;