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.