srs{enb,ue}: Use lowcase UHD as rf_type string

Older versions of srsLTe.git required passing UHD in caps to the conf
file, but that's not the case anymore. Let's use lowcase then.

Change-Id: If8a289ba110229d31b62b0d3adc1ae97324e6d27

example/resources.conf.prod

@@ -164,7 +164,7 @@ enb:
 
 - label: srsENB-B200
   type: srsenb
-  rf_dev_type: UHD
+  rf_dev_type: uhd
   rf_dev_args: "type=b200,serial=306BD11"
   remote_user: jenkins
   addr: 10.42.42.117

src/osmo_gsm_tester/srs_enb.py

@@ -24,7 +24,7 @@ from . import log, util, config, template, process, remote
 from . import enb
 
 def rf_type_valid(rf_type_str):
-    return rf_type_str in ('zmq', 'UHD', 'soapy', 'bladeRF')
+    return rf_type_str in ('zmq', 'uhd', 'soapy', 'bladerf')
 
 #reference: srsLTE.git srslte_symbol_sz()
 def num_prb2symbol_sz(num_prb):

src/osmo_gsm_tester/srs_ue.py

@@ -26,7 +26,7 @@ from .event_loop import MainLoop
 from .ms import MS
 
 def rf_type_valid(rf_type_str):
-    return rf_type_str in ('zmq', 'UHD', 'soapy', 'bladeRF')
+    return rf_type_str in ('zmq', 'uhd', 'soapy', 'bladerf')
 
 #reference: srsLTE.git srslte_symbol_sz()
 def num_prb2symbol_sz(num_prb):