hwmon: (scmi) Fix potential buffer overflow in scmi_hwmon_probe()

SMATCH detected a potential buffer overflow in the manipulation of
hwmon_attributes array inside the scmi_hwmon_probe function:

drivers/hwmon/scmi-hwmon.c:226
 scmi_hwmon_probe() error: buffer overflow 'hwmon_attributes' 6 <= 9

Fix it by statically declaring the size of the array as the maximum
possible as defined by hwmon_max define.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20200715121338.GA18761@e119603-lin.cambridge.arm.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>