Fixing checks for dma mapping error in qset_fill_page_list(),
I have missed two similar problems in qset_add_urb_sg() and
in qset_add_urb_sg_linearize().

v2: check validity of dma_addr with dma_mapping_error()
in qset_free_std() as suggested by Vladimir Zapolskiy.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>