Previous code was failing when reading back the timer less than
400us after resetting it. This lead nand operations to incorrectly
timeout any now and then.  Moreover, writing the load register isn't
immediately reflected in the value register. We must wait for a clock
edge, so read_timer now waits for the value to change at least once,
otherwise nand operation would timeout anyways (though less frequently).
Signed-off-by: NAlessandro Rubini <rubini@unipv.it>
Acked-by: NAndrea Gallo <andrea.gallo@stericsson.com>