[ARM] Fix Acorn platform SCSI driver build failures

SCSI folk forgot to fix up all the uses of 'buffer' before deleting
this struct member.  Do it for them to rescue the resulting build
failures.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/scsi/arm/scsi.h

@@ -74,7 +74,7 @@ static inline void init_SCp(Scsi_Cmnd *SCpnt)
 		unsigned long len = 0;
 		int buf;
 
-		SCpnt->SCp.buffer = (struct scatterlist *) SCpnt->buffer;
+		SCpnt->SCp.buffer = (struct scatterlist *) SCpnt->request_buffer;
 		SCpnt->SCp.buffers_residual = SCpnt->use_sg - 1;
 		SCpnt->SCp.ptr = (char *)
 			 (page_address(SCpnt->SCp.buffer->page) +