[GFS2] Tidy up 0 initialisations in inode.c

We don't need to use endian conversions for 0 initialisations
when creating a new on-disk inode.

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>