meta-phosphor: adjust default DISTRO_CODENAME to scarthgap

The next poky release is scarthgap.  Update our DISTRO_CODENAME to
match.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I1ffcd141a7a2d51fd693f25e191a89a469d4adf7
diff --git a/meta-phosphor/conf/distro/include/phosphor-base.inc b/meta-phosphor/conf/distro/include/phosphor-base.inc
index d04cafa..7ded76d 100644
--- a/meta-phosphor/conf/distro/include/phosphor-base.inc
+++ b/meta-phosphor/conf/distro/include/phosphor-base.inc
@@ -2,7 +2,7 @@
 require conf/distro/include/phosphor-pkg-tweaks.inc
 
 # Match the distro codename from upstream poky.
-DISTRO_CODENAME ?= "mickledore"
+DISTRO_CODENAME ?= "scarthgap"
 
 # Override these in poky based distros
 POKY_DEFAULT_DISTRO_FEATURES = "opengl ptest multiarch wayland vulkan"