arch/avr32: Fix build failure for avr32 caused by typo

This patch fixes a build failure introduced by the patch
  atmel-mci: change use of dma slave interface by Nicolas Ferre
by changing mci_dma_slave to the correct name of mci_dma_data

This should make the avr32 tree build again.

References:
http://kisskb.ellerman.id.au/kisskb/buildresult/1893610/
http://git.kernel.org/?p=linux/kernel/git/sfr/linux-next.git;a=commitdiff;h=2635d1ba711560d521f6218c585a3e0401f566e1



Patch against Linus' tree.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>