net: asix: add proper error handling of usb read errors

In the Linux kernel, the following vulnerability has been resolved: net: asix: add proper error handling of usb read errors Syzbot once again hit uninit value in asix driver. The problem still the same -- asix_read_cmd() reads less bytes, than was requested by caller. Since all read requests are performed via asix_read_cmd() let's catch usb related error there and add __must_check notation to be sure all callers actually check return value. So, this patch adds sanity check inside asix_read_cmd(), that simply checks if bytes read are not less, than was requested and adds missing error handling of asix_read_cmd() all across the driver code.