iio:bma180: Use iio_push_buffers_with_timestamp()

Makes the code shorter and a bit less ugly.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: Oleksandr Kravchenko <o.v.kravchenko@globallogic.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>