s390/crash: fix incorrect number of bytes to copy to user space

The number of bytes in a chunk is correctly calculated, but instead
the total number of bytes is passed to copy_to_user_real() function.
Reported-by: Matthew Wilcox <willy@infradead.org>
Fixes: df9694c7 ("s390/dump: streamline oldmem copy functions")
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/kernel/crash_dump.c

@@ -199,7 +199,7 @@ static int copy_oldmem_user(void __user *dst, unsigned long src, size_t count)
 			} else {
 				len = count;
 			}
-			rc = copy_to_user_real(dst, src, count);
+			rc = copy_to_user_real(dst, src, len);
 			if (rc)
 				return rc;
 		}