[media] rtl2832_sdr: cleanup some set_bit() calls

This code works fine but static checkers complain.  The test_bit()
function takes the bit number and not a mask.  Then the other issue is
that we were using USB_STATE_URB_BUF which is BIT(0) instead of URB_BUF.
Also we were open coding that instead of using the test/clear/set_bit()
functions.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>