ddr: altera: Clean up rw_mgr_mem_calibrate_vfifo_center() part 2

Factor out common code from rw_mgr_mem_calibrate_writes_center()
and rw_mgr_mem_calibrate_vfifo_center() for searching for the
left edge of the window. The code is almost identical, so pull
it into separate function and cater for the minor differences.

Signed-off-by: Marek Vasut <marex@denx.de>
1 file changed