Whether reset_source_name() returns the just set reset_source is
dependent on probe order and the priorities of prior reset sources
in relation to the current one. Make this more robust by using the new
reset_source_to_string.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>