powerpc/85xx: Fix SRIO LAW setup on corenet_ds boards

In function board_early_init_r(), serdes will not be initialize yet.
Thus sRIO was always considered disabled.  Move the check for sRIO into
misc_init_r() which is called after fsl_serdes_init().

Also, fixed warning associated with gur variable possibly not being
used.

Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Signed-off-by: Lian Minghuan <B31939@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>