dmaengine: xgene-dma: remove unused xgene_dma_invalidate_buffer

Commit c678fa66: ("dmaengine: remove DMA_SG as it is dead code in
kernel") removes DMA_SG from dmaengine subsystem but missed removing unused
xgene_dma_invalidate_buffer function, so remove it

drivers/dma/xgene-dma.c:394:13: warning: ‘xgene_dma_invalidate_buffer’ defined but not used [-Wunused-function]
 static void xgene_dma_invalidate_buffer(__le64 *ext8)
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/xgene-dma.c

@@ -391,11 +391,6 @@ static void xgene_dma_set_src_buffer(__le64 *ext8, size_t *len,
 	*paddr += nbytes;
 }
 
-static void xgene_dma_invalidate_buffer(__le64 *ext8)
-{
-	*ext8 |= cpu_to_le64(XGENE_DMA_INVALID_LEN_CODE);
-}
-
 static __le64 *xgene_dma_lookup_ext8(struct xgene_dma_desc_hw *desc, int idx)
 {
 	switch (idx) {