x86: pci-swiotlb.c swiotlb_dma_ops should be static

Impact: reduce kernel size a bit, address sparse warning

Addresses the problem pointed out by this sparse warning:

  arch/x86/kernel/pci-swiotlb.c:53:20: warning: symbol 'swiotlb_dma_ops' was not declared. Should it be static?

For x86: swiotlb_dma_ops can be static, because it's not used outside
of pci-swiotlb.c

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
LKML-Reference: <1239558861.3938.2.camel@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>