ASoC: mpc5200: remove duplicate identical IRQ handler

The TX and RX irq handlers are identical.  Merge them

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>