opentitan: Update toolchain paths to match $(OUT)/cache
opentitan: Update toolchain paths to match $(OUT)/cache

Change-Id: Id86e9c2dc64d7c04e2961e6d1722b689aa322c11
GitOrigin-RevId: 451a7e023b7b703f495ba4ca0f08c44aedd8116c

AmbiML/sparrow-build