net: dsa: fix a crash if ->getssetcount() fails
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.19.193 by commit 0f2cb08c57edefb0e7b5045e0e3e9980a3d3aa37, it was introduced in version v4.7 by commit badf3ada60ab8f76f9488dc8f5c0c57f70682f5a. For more details please see the references link.