colibri_vf: Fix bstlen field

Commit 3f353cecc ("vf610: refactor DDRMC code") changed the original
bstlen field from 3 to 0.

Restore the original value for proper behaviour.

Based on the patch from Anthony Felice <tony.felice@timesys.com>
for the vf610twr board.

Reported-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

board/toradex/colibri_vf/colibri_vf.c

@@ -119,7 +119,7 @@ int dram_init(void)
 		.trcd_int          = 6,
 		.tras_lockout      = 0,
 		.tdal              = 12,
-		.bstlen            = 0,
+		.bstlen            = 3,
 		.tdll              = 512,
 		.trp_ab            = 6,
 		.tref              = 3120,