i2c: core: only use set_scl for bus recovery after calling prepare_recovery

Using set_scl may be ineffective before calling the driver specific
prepare_recovery callback, which might change into a test mode. So
instead of setting SCL in i2c_generic_scl_recovery, move it to
i2c_generic_recovery (after the optional prepare_recovery).

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Acked-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>