arm: mvebu: turris_omnia: fix leaked mtd device

After getting MTD device via get_mtd_device_nm(), we need to put it with
put_mtd_device(), otherwise we get

  Removing MTD device #0 (mx25l6405d) with use count 1

before booting kernel.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Pali Rohár <pali@kernel.org>
Tested-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/board/CZ.NIC/turris_omnia/turris_omnia.c b/board/CZ.NIC/turris_omnia/turris_omnia.c
index bac78af..a48e1f5 100644
--- a/board/CZ.NIC/turris_omnia/turris_omnia.c
+++ b/board/CZ.NIC/turris_omnia/turris_omnia.c
@@ -647,10 +647,13 @@
 	if (!fixup_mtd_partitions(blob, node, mtd))
 		goto fail;
 
+	put_mtd_device(mtd);
 	return 0;
 
 fail:
 	printf("Failed fixing SPI NOR partitions!\n");
+	if (!IS_ERR_OR_NULL(mtd))
+		put_mtd_device(mtd);
 	return 0;
 }
 #endif