kernel-devsrc: fix QA warning about empty /usr/src

OE throws a QA warning during kernel-devsrc-*:do_package, about the
/usr/src directory not being installed into any package. When alternate
kernel-devsrc packages remove the /usr/src/kernel symlink, the /usr/src
path in the package install root becomes empty, and so triggers the
warning.

Try to remove the path from the install root, to satisfy OE.

Signed-off-by: Alex Stewart <[email protected]>

recipes-kernel/linux/kernel-devsrc-nilrt-alternate.inc

@@ -5,5 +5,6 @@ do_install_append() {
    # Remove the symlink so it doesn't conflict with other
    # kernel-devsrc packages
    rm -f ${D}/usr/src/kernel
+   rmdir --ignore-fail-on-non-empty ${D}/usr/src
 }