GN build: replace magma.gni vars in Lavapipe

This was missed in the previous CL; Lavapipe wasn't built in CQ.

Change-Id: I4f1c016c0fa616cd527a97f7601031659729f1c8
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1029238
Reviewed-by: Craig Stout <cstout@google.com>
Fuchsia-Auto-Submit: Josh Gargus <jjosh@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
diff --git a/src/gallium/frontends/lavapipe/BUILD.gn b/src/gallium/frontends/lavapipe/BUILD.gn
index 905fc67..85618fa 100644
--- a/src/gallium/frontends/lavapipe/BUILD.gn
+++ b/src/gallium/frontends/lavapipe/BUILD.gn
@@ -158,8 +158,8 @@
 
   deps = [
     # See target-level comment for rationale of use of Magma in Lavapipe.
-    "$magma_build_root/src/libmagma:magma_sysmem",
     "$mesa_build_root/include:vulkan",
+    "//src/graphics/lib/magma/src/libmagma:magma_sysmem",
     "//src/graphics/magma/lib/magma/platform/zircon:logger_for_stderr",
   ]