mb/google/volteer: set DRAM Max Cycle Time to 15

The DRAM Max Cycle Time (tCKmax) for Samsung's K4UBE3D4AA-MGCL DRAM
part should be set to 0xF.

BUG=b:157178553, b:156555863
TEST="emerge-volteer coreboot chromeos-bootimage", flash and boot a
SKU4 volteer to the kernel and run "memtester 6G 100" and verify it
completes successfully without error and does not crash.

Change-Id: Id95b19fe261e3f57a52a43055acab99af66b14ab
Signed-off-by: Nick Vaccaro <nvaccaro@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41634
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/google/volteer/variants/volteer/spd/SPD_LPDDR4X_200b_8bank_2Rx16_32Gb_DDP_4267.spd.hex b/src/mainboard/google/volteer/variants/volteer/spd/SPD_LPDDR4X_200b_8bank_2Rx16_32Gb_DDP_4267.spd.hex
index 90202f9..778967d 100644
--- a/src/mainboard/google/volteer/variants/volteer/spd/SPD_LPDDR4X_200b_8bank_2Rx16_32Gb_DDP_4267.spd.hex
+++ b/src/mainboard/google/volteer/variants/volteer/spd/SPD_LPDDR4X_200b_8bank_2Rx16_32Gb_DDP_4267.spd.hex
@@ -1,5 +1,5 @@
 23 11 11 0E 15 21 B5 08 00 00 00 00 0A 01 00 00
-48 00 04 00 92 54 05 00 87 00 90 A8 90 C0 08 60
+48 00 04 0F 92 54 05 00 87 00 90 A8 90 C0 08 60
 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00