skiboot-5.3.0-rc1 for firenze, garrison and p9_mambo

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/configs/garrison_defconfig b/openpower/configs/garrison_defconfig
index 4a9f46a..6bb0868 100644
--- a/openpower/configs/garrison_defconfig
+++ b/openpower/configs/garrison_defconfig
@@ -33,7 +33,7 @@
 
 # skiboot requirements
 BR2_SKIBOOT_CUSTOM_VERSION=y
-BR2_SKIBOOT_CUSTOM_VERSION_VALUE="68b4d66bdad8bc036073d1a4cbc26e94cdaf908a"
+BR2_SKIBOOT_CUSTOM_VERSION_VALUE="skiboot-5.3.0-rc1"
 
 # petitboot requirements
 BR2_ENABLE_LOCALE_PURGE=y