nb/intel/x4x/raminit: Fix DIMM_IN_CHANNEL calculation

Fix-up for 696abfc
  nb/intel/x4x: Fix and deflate `dimm_config` in raminit

It didn't fix the channel-number shifting issue as intended.

The channel index is either 0 or 1. DIMMs are counted from 0
to 3 where 0..1 covers channel 0, and 2..3 covers channel 1.
Since we have two DIMMs per channel, we have to multiply the
channel index by 2 (or shift it left by 1) to get the index
of the first DIMM in the channel. Finally, to get the offset
of a DIMM in the channel we take its index modulo 2 (again,
the number of DIMMs per channel).

Change-Id: I2784b0cb655bfe823bf5fa48b722623dfca1ddc3
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/17612
Tested-by: build bot (Jenkins)
Reviewed-by: Damien Zammit <damien@zamaudio.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/northbridge/intel/x4x/raminit.c

@@ -153,7 +153,8 @@ static void sdram_read_spds(struct sysinfo *s)
 				else
 					die("Dual-rank x16 not supported\n");
 			}
-			s->dimm_config[chan] |= dimm_config << (i - chan) * 2;
+			s->dimm_config[chan] |=
+				dimm_config << (i % DIMMS_PER_CHANNEL) * 2;
 		}
 		printk(BIOS_DEBUG, "  Config[CH%d] : %d\n", chan, s->dimm_config[chan]);
 	}