daemon: Fix part-to-dev when the partition name includes p<N>.

If the device name ends with a number, Linux uses partition names of
the form <device>p<N>.  Handle this case by knocking off the 'p'
character.

daemon/devsparts.c

@@ -203,6 +203,9 @@ do_part_to_dev (const char *part)
     return NULL;
   }
 
+  if (part[n-1] == 'p')
+    n--;
+
   char *r = strndup (part, n);
   if (r == NULL) {
     reply_with_perror ("strdup");