Switch to pw_sys_io_rp2040 backend

Change-Id: I256ae89d6e961ffc80ec9f0328848157625a297d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/kudzu/+/191470
Reviewed-by: Anthony DiGirolamo <tonymd@google.com>
Commit-Queue: Erik Gilling <konkers@google.com>
diff --git a/targets/rp2040/BUILD.gn b/targets/rp2040/BUILD.gn
index 71be1b6..661f954 100644
--- a/targets/rp2040/BUILD.gn
+++ b/targets/rp2040/BUILD.gn
@@ -63,7 +63,7 @@
     pw_third_party_freertos_CONFIG = "//targets/rp2040:freertos_config"
     pw_third_party_freertos_PORT = "$dir_pw_third_party/freertos:arm_cm0"
 
-    pw_sys_io_BACKEND = dir_pw_sys_io_stdio
+    pw_sys_io_BACKEND = dir_pw_sys_io_rp2040
 
     pw_build_LINK_DEPS += [
       "//targets/rp2040:pre_init",