BUILD: cache: fix non-inline vs inline declaration mismatch to silence a warning

BUILD: cache: fix non-inline vs inline declaration mismatch to silence a warning

Some compilers report this on the cache:
  src/cache.c:235: warning: 'release_entry_locked' declared inline after being called
  src/cache.c:235: warning: previous declaration of 'release_entry_locked' was here

And indeed, the function is first declared non-inline and later inline.
Let's just set the inline status from the beginning. It's not really
needed to backport this.