x86_64/traps: Fix always true condition

We should be checking IS_ERR() here.  PTR_ERR() is always true.

Fixes: fe3d197f8431 ('x86, mpx: On-demand kernel allocation of
bounds tables')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Link: http://lkml.kernel.org/r/20141125172114.GA24535@mwanda
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/traps.c

@@ -323,7 +323,7 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 		break; /* Success, it was handled */
 	case 1: /* Bound violation. */
 		info = mpx_generate_siginfo(regs, xsave_buf);
-		if (PTR_ERR(info)) {
+		if (IS_ERR(info)) {
 			/*
 			 * We failed to decode the MPX instruction.  Act as if
 			 * the exception was not caused by MPX.