ext4: fix special inode number checks in __ext4_iget()

The check for special (reserved) inode number checks in __ext4_iget()
was broken by commit 8a363970: ("ext4: avoid declaring fs
inconsistent due to invalid file handles").  This was caused by a
botched reversal of the sense of the flag now known as
EXT4_IGET_SPECIAL (when it was previously named EXT4_IGET_NORMAL).
Fix the logic appropriately.

Fixes: 8a363970

 ("ext4: avoid declaring fs inconsistent...")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable@kernel.org