binder: fix binder_alloc kernel-doc warnings

binder: fix binder_alloc kernel-doc warnings

Update the kernel-doc section of struct binder_alloc to fix the
following warnings reported by ./scripts/kernel-doc:

  warning: Function parameter or member 'mutex' not described in 'binder_alloc'
  warning: Function parameter or member 'vma_addr' not described in 'binder_alloc'

No functional changes in this patch.

Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Acked-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20220906135948.3048225-4-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>