fsopen: use square brackets around "fscontext"

Make the name of the anon inode fd "[fscontext]" instead of "fscontext".
This is minor but most core-kernel anon inode fds carry square brackets
around their name (cf. [1]). For the sake of consistency lets do the same
for the mount api:


Signed-off-by: Christian Brauner <christian@brauner.io>
diff --git a/fs/fsopen.c b/fs/fsopen.c
index a38fa8c..83d0d20 100644
--- a/fs/fsopen.c
+++ b/fs/fsopen.c
@@ -92,7 +92,7 @@
 	int fd;
-	fd = anon_inode_getfd("fscontext", &fscontext_fops, fc,
+	fd = anon_inode_getfd("[fscontext]", &fscontext_fops, fc,
 			      O_RDWR | O_CLOEXEC);
 	if (fd < 0)