meta-phosphor: adjust default DISTRO_CODENAME

When upstream adjusted this to mickledore, we missed it and it was still
listed as langdale.  Adjust to match.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I5ad4a373f4d4c823ecf9314218c73faf7f23213f
diff --git a/meta-phosphor/conf/distro/include/phosphor-base.inc b/meta-phosphor/conf/distro/include/phosphor-base.inc
index 3a1a56f..49d5aa3 100644
--- a/meta-phosphor/conf/distro/include/phosphor-base.inc
+++ b/meta-phosphor/conf/distro/include/phosphor-base.inc
@@ -1,7 +1,7 @@
 require conf/distro/include/phosphor-defaults.inc
 
 # Match the distro codename from upstream poky.
-DISTRO_CODENAME ?= "langdale"
+DISTRO_CODENAME ?= "mickledore"
 
 # Override these in poky based distros
 POKY_DEFAULT_DISTRO_FEATURES = "largefile opengl ptest multiarch wayland vulkan"