83xx: searching "muram-data" by compatible property

if using CONFIG_BOOTCOUNT_LIMIT feature on a MPC8360 CPU
in the muram-data node, the reg entry needs to be updated.
This is done in fdt_fixup_muram(), but we should use
the compatible "fsl,qe-muram-data" for searching the
node instead of searching the muram-data node with
an absolute path.

Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>