Bump POWER9 skiboot

Upstream skiboot now has enough code and work-arounds to boot on
POWER9 hardware with a hostboot IPL.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/configs/zaius_defconfig b/openpower/configs/zaius_defconfig
index f4f6774..ecd3cdf 100644
--- a/openpower/configs/zaius_defconfig
+++ b/openpower/configs/zaius_defconfig
@@ -55,7 +55,7 @@
 BR2_OCC_BIN_FILENAME="occ.bin"
 BR2_CAPP_UCODE_BIN_FILENAME="cappucode.bin"
 BR2_SKIBOOT_CUSTOM_VERSION=y
-BR2_SKIBOOT_CUSTOM_VERSION_VALUE="ca4a1ee53c0081020b0330acc6f4bcf446bccbbd"
+BR2_SKIBOOT_CUSTOM_VERSION_VALUE="28e96ffaba8b659f48312bdcea35a1403310fba3"
 BR2_PACKAGE_LOADKEYS=y
 BR2_ZAIUS_SYSTEM_XML_FILENAME="ZAIUS_hb.system.xml"
 BR2_ZAIUS_MRW_XML_FILENAME="ZAIUS_hb.mrw.xml"