mmc: Fix error in RPMB code

Since we do not build any board with CONFIG_SUPPORT_EMMC_RPMB , this
piece of code evaded conversion. Fix the following compiler error:

cmd/mmc.c: In function 'do_mmcrpmb':
cmd/mmc.c:316:32: error: 'struct blk_desc' has no member named 'part_num'
  original_part = mmc->block_dev.part_num;
                                ^

Signed-off-by: Marek Vasut <[email protected]>
Cc: Pantelis Antoniou <[email protected]>
Cc: Tom Rini <[email protected]>

cmd/mmc.c

@@ -313,7 +313,7 @@ static int do_mmcrpmb(cmd_tbl_t *cmdtp, int flag,
 		return CMD_RET_FAILURE;
 	}
 	/* Switch to the RPMB partition */
-	original_part = mmc->block_dev.part_num;
+	original_part = mmc->block_dev.hwpart;
 	if (mmc_select_hwpart(curr_device, MMC_PART_RPMB) != 0)
 		return CMD_RET_FAILURE;
 	ret = cp->cmd(cmdtp, flag, argc, argv);