bcachefs: fix typo in reference to BCACHEFS_DEBUG

Commit ec9cc18f ("bcachefs: Add checks for invalid snapshot IDs")
intends to check the sanity of a snapshot and panic when
BCACHEFS_DEBUG is set, but that conditional has a typo.

Fix the typo to refer to the actual existing Kconfig symbol.

This was found with ./scripts/checkkconfigsymbols.py.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/snapshot.h

@@ -77,7 +77,7 @@ static inline u32 __bch2_snapshot_parent(struct bch_fs *c, u32 id)
 		return 0;
 
 	u32 parent = s->parent;
-	if (IS_ENABLED(CONFIG_BCACHEFS_DEBU) &&
+	if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG) &&
 	    parent &&
 	    s->depth != snapshot_t(c, parent)->depth + 1)
 		panic("id %u depth=%u parent %u depth=%u\n",