staging: ti-soc-thermal: propagate error code

While writing talert thresholds, propagate the error code from
ti_bandgap_update_alert_threshold to the caller of
_ti_bandgap_write_threshold.

Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>