proc: copy_to_user() returns unsigned

copy_to_user() returns the number of bytes left to be copied.

This was a typo from: d82ef020cf31 "proc: pagemap: Hold mmap_sem during
page walk".

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/task_mmu.c

@@ -800,7 +800,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 		start_vaddr = end;
 
 		len = min(count, PM_ENTRY_BYTES * pm.pos);
-		if (copy_to_user(buf, pm.buffer, len) < 0) {
+		if (copy_to_user(buf, pm.buffer, len)) {
 			ret = -EFAULT;
 			goto out_free;
 		}