driver/ddr/fsl: Fix timing_cfg_2

Commit 5605dc61 tried to fix wr_lat bit in timing_cfg_2, but the
change was wrong. wr_lat has 5 bits with MSB at [13] and lower
4 bits at [9:12], in big-endian convention.

Signed-off-by: York Sun <york.sun@nxp.com>
Reported-by: Thomas Schaefer <Thomas.Schaefer@kontron.com>