artemis_svl: Only print serial error message on SerialException

The catch all `except:` masks other errors.

Author: konkers

tools/artemis/artemis_svl.py

@@ -335,7 +335,7 @@ def main():
             if( bl_failed == False ):
                 break
 
-    except:
+    except serial.SerialException:
         phase_serial_port_help()
 
     exit()