USB: g_printer bugfixes

G_PRINTER: Bug fix for blocking reads and a fix for a memory leak.

This fixes bugs in blocking IO calls. When the poll() entry point
is called receive transfers will be setup if they have not already
been. Another bug fix is that the poll() entry point now checks the
current receive buffer for data when reporting if any data had been
received. A memory leak was fixed that could have occurred when a
USB reset happened.

Signed-off-by: Craig W. Nadler <craig@nadler.us>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>