[rawfs] Fix crash if bogus is unset

- fixes:
	12:44:25 [6]: Python Error:
	 <class 'TypeError'>
	 'builtin_function_or_method' object is not subscriptable
	 File "/usr/lib/calamares/modules/rawfs/main.py", line 188, in run
	    item.copy(filesystems.index(item), len(filesystems))

	  File "/usr/lib/calamares/modules/rawfs/main.py", line 99, in copy
	    if libcalamares.job.configuration["bogus"]:

src/modules/rawfs/main.py

@@ -96,7 +96,7 @@ class RawFSItem:
         count = 0
 
         libcalamares.utils.debug("Copying {} to {}".format(self.source, self.destination))
-        if libcalamares.job.configuration["bogus"]:
+        if libcalamares.job.configuration.get("bogus", False):
             return
 
         srcsize, srcblksize = get_device_size(self.source)