intel/broadwell: "free" memory after use

While we stub out free(), tools like coverity scan have no idea, and it
might change in the future. So free it.

Change-Id: I1d93a6f45b64445662daa95b51128140ad0a87e2
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Found-by: Coverity Scan #1260716
Reviewed-on: https://review.coreboot.org/17055
Tested-by: build bot (Jenkins)
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

src/soc/intel/broadwell/me.c

@@ -966,6 +966,7 @@ static int intel_me_read_mbp(me_bios_payload *mbp_data, device_t dev)
 	}
 	#undef ASSIGN_FIELD_PTR
 
+	free(mbp);
 	return ret;
 }