swiotlb: Remove the swiotlb variable usage

POWERPC doesn't expect it to be used.

This fixes the linux-next build failure reported by
Stephen Rothwell:

  lib/swiotlb.c: In function 'setup_io_tlb_npages':
  lib/swiotlb.c:114: error: 'swiotlb' undeclared (first use in this function)

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: peterz@infradead.org
LKML-Reference: <20091112000258F.fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/include/asm/swiotlb.h b/arch/x86/include/asm/swiotlb.h
index b9e4e20..940f13a 100644
--- a/arch/x86/include/asm/swiotlb.h
+++ b/arch/x86/include/asm/swiotlb.h
@@ -9,11 +9,12 @@
 
 #ifdef CONFIG_SWIOTLB
 extern int swiotlb;
-extern void pci_swiotlb_init(void);
+extern int pci_swiotlb_init(void);
 #else
 #define swiotlb 0
-static inline void pci_swiotlb_init(void)
+static inline int pci_swiotlb_init(void)
 {
+	return 0;
 }
 #endif