thermal: stm32: Fix stm_thermal_read_factory_settings

Adding brackets allows to multiply the register value,
masked by TS1_RAMP_COEFF_MASK, by an ADJUST value
properly and not to multiply ADJUST by register value and
then mask the whole.

Fixes: 1d693155 ("thermal: add stm32 thermal driver")
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: David Hernandez Sanchez <david.hernandezsanchez@st.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>