Transceiver52M: UHD: Add string descriptors to device-offset pairs

As we add more channel combintions including but not limited to
new devices, signal processing schemes, and diversity, we'll
need to handle more special cases. Add string descriptions for
just a bit more sanity.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
diff --git a/Transceiver52M/UHDDevice.cpp b/Transceiver52M/UHDDevice.cpp
index a2c2471..681f939 100644
--- a/Transceiver52M/UHDDevice.cpp
+++ b/Transceiver52M/UHDDevice.cpp
@@ -52,6 +52,7 @@
 	enum uhd_dev_type type;
 	int sps;
 	double offset;
+	const std::string desc;
 };
 
 /*
@@ -65,16 +66,16 @@
  *   USRP1 with timestamps is not supported by UHD.
  */
 static struct uhd_dev_offset uhd_offsets[NUM_USRP_TYPES * 2] = {
-	{ USRP1, 1, 0.0 },
-	{ USRP1, 4, 0.0 },
-	{ USRP2, 1, 1.2184e-4 },
-	{ USRP2, 4, 8.0230e-5 },
-	{ B100,  1, 1.2104e-4 },
-	{ B100,  4, 7.9307e-5 },
-	{ B2XX,  1, 9.9692e-5 },
-	{ B2XX,  4, 6.9248e-5 },
-	{ UMTRX, 1, 9.9692e-5 },
-	{ UMTRX, 4, 7.3846e-5 },
+	{ USRP1, 1,       0.0, "USRP1 not supported" },
+	{ USRP1, 4,       0.0, "USRP1 not supported"},
+	{ USRP2, 1, 1.2184e-4, "N2XX 1 SPS" },
+	{ USRP2, 4, 8.0230e-5, "N2XX 4 SPS" },
+	{ B100,  1, 1.2104e-4, "B100 1 SPS" },
+	{ B100,  4, 7.9307e-5, "B100 4 SPS" },
+	{ B2XX,  1, 9.9692e-5, "B2XX 1 SPS" },
+	{ B2XX,  4, 6.9248e-5, "B2XX 4 SPS" },
+	{ UMTRX, 1, 9.9692e-5, "UmTRX 1 SPS" },
+	{ UMTRX, 4, 7.3846e-5, "UmTRX 4 SPS" },
 };
 
 static double get_dev_offset(enum uhd_dev_type type, int sps)