MAINTAINERS: Add cfriedt as C library collaborator

Add myself as collaborator on the C library.

Signed-off-by: Christopher Friedt <cfriedt@fb.com>
diff --git a/MAINTAINERS.yml b/MAINTAINERS.yml
index d4c402f..0f23b38 100644
--- a/MAINTAINERS.yml
+++ b/MAINTAINERS.yml
@@ -295,6 +295,7 @@
          - enjiamai
          - KangJianX
          - keith-packard
+         - cfriedt
     files:
          - lib/libc/
          - tests/lib/c_lib/