ia64: fix build failure with CONFIG_SWIOTLB

arch/ia64/kernel/pci-swiotlb.c is removed in commit 4fac8076 ("ia64: clean up swiotlb support")
but pci-swiotlb.o is still present in Makefile, and so build fail when
CONFIG_SWIOTLB is enabled.
Fix the build failure by removing pci-swiotlb.o from makefile

Fixes: 4fac8076 ("ia64: clean up swiotlb support")
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>