uhd: remove external clock polarity setting

Unused and causes the follwing errors on certain UHD versions.

"ValueError: unhandled clock configuration reference source: _external_"

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

git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2664 19bc5d8c-e614-43d4-8b26-e1612bc8e597
diff --git a/Transceiver52M/UHDDevice.cpp b/Transceiver52M/UHDDevice.cpp
index f319ba6..ef5b2fc 100644
--- a/Transceiver52M/UHDDevice.cpp
+++ b/Transceiver52M/UHDDevice.cpp
@@ -278,7 +278,6 @@
 	uhd::clock_config_t clk_cfg;
 
 	clk_cfg.pps_source = uhd::clock_config_t::PPS_SMA;
-	clk_cfg.pps_polarity = uhd::clock_config_t::PPS_NEG;
 
 	if (ext_clk)
 		clk_cfg.ref_source = uhd::clock_config_t::REF_SMA;