bdaddr_read.c: Don't call property_get with too small buffer

It's an error to call property_get with too small of a buffer.
Pass a large enough buffer, and do checks to make sure the returned
value isn't too big.

Change-Id: Ia3ebb85deb856496b3d16a2ef604878b2ebe2bce
Signed-off-by: David Rodero <david@codiguiel.net>