meta-toolchain-osmo: Include without direct addresssing

Use the BBPATH to find the recipe instead of assuming where this
layer has been placed.
diff --git a/recipes-osmocom/meta/meta-toolchain-osmo.bb b/recipes-osmocom/meta/meta-toolchain-osmo.bb
index a8cd442..336e95f 100644
--- a/recipes-osmocom/meta/meta-toolchain-osmo.bb
+++ b/recipes-osmocom/meta/meta-toolchain-osmo.bb
@@ -3,4 +3,4 @@
 TOOLCHAIN_TARGET_TASK = "${TOOLCHAIN_TARGET_OSMOTASK}"
 TOOLCHAIN_OUTPUTNAME = "${SDK_NAME}-toolchain-osmo-${DISTRO_VERSION}"
 PROVIDES = "meta-toolchain-sdk"
-require ../../../meta/recipes-core/meta/meta-toolchain.bb
+require recipes-core/meta/meta-toolchain.bb