powerpc/dts: fix sRIO error interrupt for b4860

For B4 platform, MPIC EISR register is in reversed bitmap order,
instead of "Error interrupt source 0-31. Bit 0 represents SRC0."
the correct ordering is "Error interrupt source 0-31. Bit 0
represents SRC31." This patch is to fix sRIO EISR bit value
of error interrupt in dts node.

Signed-off-by: Minghuan Lian <Minghuan.Lian@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>