When getting the string descriptors, fetch 2 bytes (size and type) first,

When getting the string descriptors, fetch 2 bytes (size and type) first,
and then the whole string based on the returned size, not just one byte.
The Lexar card reader kindly loaned by
Denis Doroshenko (denis dot doroshenko at gmail.com) it's happy now, and
after further inspection it's what other OSs do.
Discussed with yuo@. krw@ yuo@ ok.