grgsm_capture: Fix device arguments

We need a space between numchan=1 and the rest of the device arguments
otherwise when --args is specified it fails with RuntimeError: bad lexical cast

$ grgsm_capture --args=soapy

Traceback (most recent call last):
  File "/usr/local/bin/grgsm_capture", line 179, in <module>
    device_args=options.device_args)
  File "/usr/local/bin/grgsm_capture", line 57, in __init__
    osmosdr.source(args="numchan=1" + device_args )
  File "/usr/local/lib64/python2.7/site-packages/osmosdr/osmosdr_swig.py", line 1170, in make
    return _osmosdr_swig.source_make(*args, **kwargs)
RuntimeError: bad lexical cast: source type value could not be interpreted as target

Change-Id: I2d1bcee835b695c91a5c44ec78a40b2d969f611c

apps/helpers/grgsm_capture

@@ -54,7 +54,8 @@ class grgsm_capture(gr.top_block):
         ##################################################
 
         self.sdr_source = \
-                    osmosdr.source(args="numchan=1" + device_args )
+                    osmosdr.source(args="numchan=" + str(1) + " " + device_args)
+
         self.sdr_source.set_sample_rate(samp_rate)
         self.sdr_source.set_center_freq(freq, 0)
         self.sdr_source.set_freq_corr(freq_corr, 0)