lx_fs: fix build errors with GCC 12

/data/genode/repos/os/src/server/lx_fs/directory.h: In member function ‘virtual Genode::size_t Lx_fs::Directory::read(char*, Genode::size_t, File_system::seek_off_t)’:
/data/genode/repos/os/src/server/lx_fs/directory.h:224:53: error: ‘dent’ may be used uninitialized [-Werror=maybe-uninitialized]
  224 |                                 .type  = type(dent->d_type),
      |                                               ~~~~~~^~~~~~
/data/genode/repos/os/src/server/lx_fs/directory.h:197:40: note: ‘dent’ was declared here
  197 |                         struct dirent *dent;
      |                                        ^~~~

Issue #4827

repos/os/src/server/lx_fs/directory.h

@@ -193,12 +193,12 @@ class Lx_fs::Directory : public Node
 
 			seek_off_t index = seek_offset / sizeof(Directory_entry);
 
-			/* seek to index and read entry */
-			struct dirent *dent;
+			/* seek to index */
 			rewinddir(_fd);
-			for (unsigned i = 0; i <= index; ++i) {
-				dent = readdir(_fd);
-			}
+			for (unsigned i = 0; i < index; ++i)
+				readdir(_fd);
+
+			struct dirent *dent = readdir(_fd);
 
 			if (!dent)
 				return 0;