ac_fs: Fix return value of ac_fs_copy()
ac_fs: Fix return value of ac_fs_copy()

The intent was to return either -1 on error or the number of bytes
written.

However we only tracked the current number of bytes written not the
overall total.

Fixes: d28cfa7 ("ac_fs: Add a file copy function")
Signed-off-by: Andrew Clayton <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@digital-domain.net>

ac000/libac