usb: properly detect empty mass storage media reader

When a USB card reader is empty, it will return "Not Ready - medium not
present" as Key Code Qualifier. In that situation, it's useless waiting
for the full timeout since the result won't change until the user
inserts a card.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>