net: fm: use get_nand_dev_by_index()

As part of preparation for nand DM conversion the new API has been
introduced to remove direct access to nand_info array. So, use it here
instead of accessing to nand_info array directly.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/fm/fm.c b/drivers/net/fm/fm.c
index 89f0d6a..9fe34ad 100644
--- a/drivers/net/fm/fm.c
+++ b/drivers/net/fm/fm.c
@@ -357,7 +357,8 @@
 	size_t fw_length = CONFIG_SYS_QE_FMAN_FW_LENGTH;
 	void *addr = malloc(CONFIG_SYS_QE_FMAN_FW_LENGTH);
 
-	rc = nand_read(nand_info[0], (loff_t)CONFIG_SYS_FMAN_FW_ADDR,
+	rc = nand_read(get_nand_dev_by_index(0),
+		       (loff_t)CONFIG_SYS_FMAN_FW_ADDR,
 		       &fw_length, (u_char *)addr);
 	if (rc == -EUCLEAN) {
 		printf("NAND read of FMAN firmware at offset 0x%x failed %d\n",