linux-libc-headers: Switch to distro-neutral openharmony override

This allows building OpenHarmony compatible linux-libc-headers using any distro
configuration which enables "openharmony" in its DISTROOVERRIDES.

Signed-off-by: Esben Haabendal <esben.haabendal@huawei.com>

recipes-kernel/linux-libc-headers/linux-libc-headers_%.bbappend

@@ -4,6 +4,6 @@
 
 # OpenHarmony relies on Android's ashmem, which is in staging and therefore
 # the header is not installed by default
-do_install:append:oniro-openharmony-linux() {
+do_install:append:openharmony() {
     install ${S}/drivers/staging/android/uapi/ashmem.h ${D}${includedir}/linux
 }