android: binder: fix a kernel-doc enum warning

Add kernel-doc notation for @LOOP_END to prevent a kernel-doc
warning.

binder_alloc_selftest.c:76: warning: Enum value 'LOOP_END' not described in enum 'buf_end_align_type'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Martijn Coenen <maco@android.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Christian Brauner <christian@brauner.io>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Acked-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20231205225324.32362-1-rdunlap@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>