ide-atapi: switch to blk_rq_bytes() on do_request() path

After the recent struct request cleanups, blk_rq_bytes() is guaranteed
to be valid and is the current total length of the rq's bio. Use that
instead of pc->req_xfer in the do_request() path after the command has
been queued

The remaining usage of pc->req_xfer now is only until we map the rq to a
bio.

While at it:

- remove local caching of rq completion length in ide_tape_issue_pc()

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
diff --git a/drivers/ide/ide-floppy.c b/drivers/ide/ide-floppy.c
index 6509817..a1c5598 100644
--- a/drivers/ide/ide-floppy.c
+++ b/drivers/ide/ide-floppy.c
@@ -210,7 +210,7 @@
 	if (rq->cmd_flags & REQ_RW)
 		pc->flags |= PC_FLAG_WRITING;
 	pc->buf = NULL;
-	pc->req_xfer = pc->buf_size = blocks * floppy->block_size;
+	pc->buf_size = blk_rq_bytes(rq);
 	pc->flags |= PC_FLAG_DMA_OK;
 }
 
@@ -227,7 +227,7 @@
 	}
 	/* pio will be performed by ide_pio_bytes() which handles sg fine */
 	pc->buf = NULL;
-	pc->req_xfer = pc->buf_size = blk_rq_bytes(rq);
+	pc->buf_size = blk_rq_bytes(rq);
 }
 
 static ide_startstop_t ide_floppy_do_request(ide_drive_t *drive,
@@ -286,8 +286,8 @@
 
 	cmd.rq = rq;
 
-	if (blk_fs_request(rq) || pc->req_xfer) {
-		ide_init_sg_cmd(&cmd, pc->req_xfer);
+	if (blk_fs_request(rq) || blk_rq_bytes(rq)) {
+		ide_init_sg_cmd(&cmd, blk_rq_bytes(rq));
 		ide_map_sg(drive, &cmd);
 	}