nb/intel/sandybridge/raminit: Add edge write discovery check

Make sure edge write test results are sane.
Check rn.all to make sure rn.start and rn.end are valid.
Most likely the following test is going to fail on the same
rank anyway.

Change-Id: Ifa601406e6c74ceb8d70063be5ce1bf6bc512c18
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/11247
Tested-by: build bot (Jenkins)
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>

src/northbridge/intel/sandybridge/raminit.c

@@ -3130,6 +3130,8 @@ static void discover_edges_write_real(ramctr_timing * ctrl, int channel,
 				upper[lane] =
 					min(rn.end - ctrl->edge_offset[i], upper[lane]);
 				edges[lane] = (lower[lane] + upper[lane]) / 2;
+				if (rn.all || (lower[lane] > upper[lane]))
+					die("edge write discovery failed");
 
 			}
 		}