x86: Remove weird PTR_ERR() in do_debug

62edab90 changed the argument to notify_die() from dr6 to &dr6,
but weirdly, used PTR_ERR() to cast it to a long.  Since dr6 is
on the stack, this is an abuse of PTR_ERR().  Cast to long, as
per kernel standard.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1371357768-4968-8-git-send-email-rusty@rustcorp.com.auSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/traps.c

@@ -437,7 +437,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 	/* Store the virtualized DR6 value */
 	tsk->thread.debugreg6 = dr6;
 
-	if (notify_die(DIE_DEBUG, "debug", regs, PTR_ERR(&dr6), error_code,
+	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code,
 							SIGTRAP) == NOTIFY_STOP)
 		goto exit;