omfs: fix uninitialized variable warning

quiet the warning:
fs/omfs/file.c: In function 'omfs_get_block':
fs/omfs/file.c:225: warning: 'new_block' may be used uninitialized in
this function

new_block is used properly by the call to omfs_grow_extent()

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Signed-off-by: Bob Copeland <me@bobcopeland.com>