uhd: keep reading on overrun or other non-fatal errors

The readSamples call does not return less than the
number of samples requested. Doing otherwise is a
fatal error. So on overruns, which are not fatal,
continue reading until the requested number of
samples is received.

Signed-off-by: Thomas Tsou <ttsou@vt.edu>

public-trunk/Transceiver52M/UHDDevice.cpp

@@ -578,7 +578,7 @@ int uhd_device::readSamples(short *buf, int len, bool *overrun,
 		case ERROR_TIMING:
 			restart(prev_ts);
 		case ERROR_UNHANDLED:
-			return 0;
+			continue;
 		}