Use skiboot master (d8830fd) for garrison

Periodically we should update the exact commit until a released skiboot
has full garrison support.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/configs/garrison_defconfig b/openpower/configs/garrison_defconfig
index 8aa9b92..3ea7aa3 100644
--- a/openpower/configs/garrison_defconfig
+++ b/openpower/configs/garrison_defconfig
@@ -32,6 +32,8 @@
 # skiboot requirements
 BR2_TARGET_SKIBOOT=y
 BR2_TARGET_SKIBOOT_EMBED_PAYLOAD=n
+BR2_SKIBOOT_CUSTOM_VERSION=y
+BR2_SKIBOOT_CUSTOM_VERSION_VALUE="d8830fd"
 
 # petitboot requirements
 BR2_ENABLE_LOCALE_PURGE=y