MIPS: Octeon: remove orphan octeon_swiotlb declaration

All uses of octeon_swiotlb were removed by
commit f39f8d0e ("MIPS/octeon: use swiotlb_init instead
of open coding it"), so remove the orphan declaration, too.
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/octeon/pci-octeon.h

@@ -64,6 +64,4 @@ enum octeon_dma_bar_type {
 extern enum octeon_dma_bar_type octeon_dma_bar_type;
 
 void octeon_pci_dma_init(void);
-extern char *octeon_swiotlb;
-
 #endif