staging : android : sync : get_unused_fd

sync.h recommends to use get_unused_fd which does not set
O_CLOEXEC while the rest of the android tree uses
get_unused_fd_flags and sets O_CLOEXEC.

The patch adjust the comment.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>