ARM: dma-mapping: fix debug messages in dmabounce code

This patch fixes the usage of uninitialized variables in dmabounce code
intoduced by commit a227fb92 ('ARM: dma-mapping: remove offset parameter
to prepare for generic dma_ops'):
arch/arm/common/dmabounce.c: In function ‘dmabounce_sync_for_device’:
arch/arm/common/dmabounce.c:409: warning: ‘off’ may be used uninitialized in this function
arch/arm/common/dmabounce.c:407: note: ‘off’ was declared here
arch/arm/common/dmabounce.c: In function ‘dmabounce_sync_for_cpu’:
arch/arm/common/dmabounce.c:369: warning: ‘off’ may be used uninitialized in this function
arch/arm/common/dmabounce.c:367: note: ‘off’ was declared here

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>