seq_buf: Use size_t for len in seq_buf_puts()

mainline inclusion
from mainline-5.0
commit 29924e50
category: bugfix
bugzilla: 5766
CVE: NA

-------------------------------------------------

Jann Horn points out that we're using unsigned int for len in
seq_buf_puts(), which could potentially overflow if we're passed a
UINT_MAX sized string.

The rest of the code already uses size_t, so we should also use that
in seq_buf_puts() to avoid any issues.

Link: http://lkml.kernel.org/r/20181019042109.8064-2-mpe@ellerman.id.au



Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>