USB: usb_get_string should check the descriptor type

This patch (as1218) fixes a problem with a radio-control joystick used
in the "walkera 4#3" helicopter.  This device responds to the initial
Get-String-Descriptor request for string 0 (which is really the list
of supported languages) by sending its config descriptor!  The
usb_get_string() routine needs to check whether it got the right
type of descriptor.

Oddly enough, this sort of check is already present in
usb_get_descriptor().  The patch changes the error code from -EPROTO
to -ENODATA, because -EPROTO shows up in so many other contexts to
indicate a hardware failure rather than a firmware error.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Guillermo Jarabo <williamjap@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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