bcachefs: journal_shutdown is EROFS, not EIO

We often filter out EROFS errors to avoid log spew after an emergency
shutdown - journal_shutdown is just another emergency shutdown error.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

fs/bcachefs/errcode.h

@@ -269,7 +269,7 @@
 	x(BCH_ERR_invalid_sb,		invalid_sb_downgrade)			\
 	x(BCH_ERR_invalid,		invalid_bkey)				\
 	x(BCH_ERR_operation_blocked,    nocow_lock_blocked)			\
-	x(EIO,				journal_shutdown)			\
+	x(EROFS,			journal_shutdown)			\
 	x(EIO,				journal_flush_err)			\
 	x(EIO,				journal_write_err)			\
 	x(EIO,				btree_node_read_err)			\