ARM: 8548/1: dma-mapping: remove arm_dma_set_mask()

arm_dma_set_mask() implements exactly the same behavior as the fallback
that dma_set_mask() takes if the set_dma_mask op is not set. Remove it
and use that fallback instead like what is already done for
dma_get_mask().

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>