cifs: Fix integer overflow while processing acregmax mount option

[ Upstream commit 7489161b1852390b4413d57f2457cd40b34da6cc ]

User-provided mount parameter acregmax of type u32 is intended to have
an upper limit, but before it is validated, the value is converted from
seconds to jiffies which can lead to an integer overflow.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 57804646 ("cifs: Add new parameter "acregmax" for distinct file and directory metadata timeout")
Signed-off-by: Murad Masimov <m.masimov@mt-integration.ru>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>