[media] pvrusb2: check kmalloc return value

 allows the driver to proceed and initialize the below two values
 even if the kmalloc() fails.
        hdw->std_info_enum.def.type_enum.value_names
        hdw->std_info_enum.def.type_enum.count

Signed-off-by: Xiaochen Wang <wangxiaochen0@gmail.com>
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>