bcachefs: Fix shift overflow in read_one_super()

Reported-by: syzbot+9f74cb4006b83e2a3df1@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/super-io.c

@@ -649,9 +649,10 @@ static int read_one_super(struct bch_sb_handle *sb, u64 offset, struct printbuf
 
 	bytes = vstruct_bytes(sb->sb);
 
-	if (bytes > 512ULL << min(BCH_SB_LAYOUT_SIZE_BITS_MAX, sb->sb->layout.sb_max_size_bits)) {
-		prt_printf(err, "Invalid superblock: too big (got %zu bytes, layout max %lu)",
-		       bytes, 512UL << sb->sb->layout.sb_max_size_bits);
+	u64 sb_size = 512ULL << min(BCH_SB_LAYOUT_SIZE_BITS_MAX, sb->sb->layout.sb_max_size_bits);
+	if (bytes > sb_size) {
+		prt_printf(err, "Invalid superblock: too big (got %zu bytes, layout max %llu)",
+			   bytes, sb_size);
 		return -BCH_ERR_invalid_sb_too_big;
 	}