board/common: switch to md5sum for images

A cut-and-paste error caused the use of sha1sum to be named .md5.
To avoid any more confusion, let's standardize on md5sum instead,
at least for now.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

board/common/post-image.sh

@@ -24,6 +24,6 @@ dir=$(dirname "$img")
 md5=$dir/$(basename "$img" .img).md5
 
 mv "$BINARIES_DIR"/rootfs.squashfs "$img"
-sha1sum "$img" > "$md5"
+md5sum "$img" > "$md5"
 
 exit $err