Suppress expected error message in fdtdump test

Since 548aea2 "fdtdump: Discourage use of fdtdump", fdtdump unconditionally
prints a message discouraging its own use except for debugging purposes.
This shows up messily in the "make check" output, so suppress it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
1 file changed