perf/x86: Fix copy_from_user_nmi() return if range is not ok

Commit 0a19684 ("perf: Fix arch_perf_out_copy_user default"),
changes copy_from_user_nmi() to return the number of
remaining bytes so that it behave like copy_from_user().

Unfortunately, when the range is outside of the process
memory, the return value  is still the number of byte
copied, eg. 0, instead of the remaining bytes.

As all users of copy_from_user_nmi() were modified as
part of commit 0a19684, the function should be
fixed to return the total number of bytes if range is
not correct.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1435001923-30986-1-git-send-email-ydroneaud@opteya.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/lib/usercopy.c

@@ -20,7 +20,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
 	unsigned long ret;
 
 	if (__range_not_ok(from, n, TASK_SIZE))
-		return 0;
+		return n;
 
 	/*
 	 * Even though this function is typically called from NMI/IRQ context