net: fm: fix build error when not using nand

If CONFIG_CMD_NAND is disabled, get_nand_dev_by_index() is not
accessible.

This fix allows the build to succeed in this case.

Signed-off-by: Francois Gervais <fgervais@distech-controls.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
1 file changed