selftests: nci: Remove the polling code to read a NCI frame

Because the virtual NCI device uses Wait Queue, the virtual device
application doesn't need to poll the NCI frame.

Signed-off-by: Bongsu Jeon <bongsu.jeon@samsung.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>