Staging: zram: make zram_read return a bio error if the device is not initialized

Make zram_read() return a bio error if the device is not initialized
instead of pretending nothing happened.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>