uboot-imx

net/fm: call fm_port_to_index() with proper checks

Some of the fm_port_to_index() callers did not check for -1 return value and
used -1 as an array index.

Signed-off-by: Marian Rotariu <marian.rotariu@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>