thermal: ti-soc-thermal: Ensure to compute thermal trend

Workaround to compute thermal trend even when update interval
is not set. This patch will ensure to compute the thermal trend
when bandgap counter delay is not set.

Signed-off-by: Ranganath Krishnan <ranganath@ti.com>
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>