fs: ext4: fix files seen as symlink during deletion

The deletion process handles special case for symlinks whose target are
small enough that it fits in struct ext2_inode.b.symlink. So no block had
been allocated. But the check of file type wrongly considered regular
files as symlink. So, no block was freed. So, the EXT4 partition could be
corrupted because of no free block available.

Signed-off-by: Corentin GUILLEVIC <corentin.guillevic@smile.fr>