ARM: pxa: balloon3: Fix build error

irq_data_get_chip() function does not exist, call irq_desc_get_chip()
instead.

Fixes: 9ec97561

 ("ARM/pxa: Prepare balloon3_irq_handler for irq argument removal")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>