brcmfmac: return error when getting invalid max_flowrings from dongle

In the Linux kernel, the following vulnerability has been resolved:

brcmfmac: return error when getting invalid max_flowrings from dongle

When firmware hit trap at initialization, host will read abnormal max_flowrings number from dongle, and it will cause kernel panic when doing iowrite to initialize dongle ring. To detect this error at early stage, we directly return error when getting invalid max_flowrings(>256).