ci: Use tinyusb's new get-deps facility

Previously we required a recursive installation of a large number of
submodules, but now those dependencies are fetched on demand and are
limited to those required for the target platform.

.github/workflows/firmware.yml

@@ -25,4 +25,4 @@ jobs:
     - name: Build Apollo firmware for ${{ matrix.target-board }}
       run: |
         cd firmware
-        APOLLO_BOARD=${{ matrix.target-board }} make all
+        APOLLO_BOARD=${{ matrix.target-board }} make get-deps all