scripts: avoid matching 'char **' as string for systemtap

When a probe argument is declared "char *" we reference the userspace
string value using 'user_string(...)' for systemtap.

Unfortunately our code generator also matches on args declared "char **"
and generates bogus code

   *cert = user_string($arg4);

which is a syntax error for systemtap.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

scripts/dtrace2systemtap.py

@@ -124,7 +124,7 @@ for file in filelist:
         for idx in range(len(argbits)):
             arg = argbits[idx]
             isstr = False
-            if 'char *' in arg:
+            if re.match(r'''.*char\s\*[^\*].*''', arg) is not None:
                 isstr = True
 
             m = re.search(r'''^.*\s\*?(\S+)$''', arg)