bcachefs: add module description to fix modpost warning

modpost produces the following warning:

WARNING: modpost: missing MODULE_DESCRIPTION() in fs/bcachefs/bcachefs.o

Add a module description for bcachefs.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/super.c

@@ -69,6 +69,7 @@
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Kent Overstreet <kent.overstreet@gmail.com>");
+MODULE_DESCRIPTION("bcachefs filesystem");
 
 #define KTYPE(type)							\
 static const struct attribute_group type ## _group = {			\