hwmon: (aspeed-pwm-tacho) Avoid possible buffer overflow

aspeed_create_fan() reads a pwm_port value using of_property_read_u32().
If pwm_port will be more than ARRAY_SIZE(pwm_port_params), there will be
a buffer overflow in
aspeed_create_pwm_port()->aspeed_set_pwm_port_enable(). The patch fixes
the potential buffer overflow.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Evgeny Novikov <novikov@ispras.ru>
Link: https://lore.kernel.org/r/20200703111518.9644-1-novikov@ispras.ru
Signed-off-by: Guenter Roeck <linux@roeck-us.net>