poky.conf: Fix typo

(From meta-yocto rev: e1f363915056b4fad52de4d597dcac5876285400)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/distro/poky.conf

@@ -1,7 +1,7 @@
 DISTRO = "poky"
 DISTRO_NAME = "Poky (Yocto Project Reference Distro)"
 DISTRO_VERSION = "2.4"
-DISTRO_CODENAME = "rockor"
+DISTRO_CODENAME = "rocko"
 SDK_VENDOR = "-pokysdk"
 SDK_VERSION := "${@'${DISTRO_VERSION}'.replace('snapshot-${DATE}','snapshot')}"