Fix architecture filter.

If we are using uname to collect the name of the architecture, we need
to filter its output to make it consistent with dpkg. This is now
happening in the right place to avoid a spurious warning on i386 builds.

Change-Id: Iae80dbfb757fc068155730686841c742acb7a6a2

lib/img-defaults

@@ -18,20 +18,19 @@ if [ -f /etc/debian_version ]; then
   _ARCH=$(dpkg --print-architecture)
 else
   _ARCH=$(uname -m)
-fi
-ARCH=${ARCH:-$_ARCH}
-
-case $ARCH in
+  case $_ARCH in
     "x86_64")
-    ARCH="amd64"
+      _ARCH="amd64"
       ;;
     "armv"*)
-    ARCH="armhf"
+      _ARCH="armhf"
       ;;
     *)
-    echo "WARNING: Unknown architecture: $ARCH"
+      echo "WARNING: Unknown architecture: $_ARCH"
       ;;
-esac
+  esac
+fi
+ARCH=${ARCH:-$_ARCH}
 export ARCH
 
 FS_TYPE=${FS_TYPE:-ext4}