hwmon: (gl520sm) Fix overflows and crash seen when writing into limit attributes

[ Upstream commit 87cdfa9d60f4f40e6d71b04b10b36d9df3c89282 ]

Writes into limit attributes can overflow due to multplications and
additions with unbound input values. Writing into fan limit attributes
can result in a crash with a division by zero if very large values are
written and the fan divider is larger than 1.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>