import_raw_vdi: normalise whitespace

$ camlp4o -printer o -no_comments ocaml/xapi/import_raw_vdi.ml | md5sum
e74faa7367f4c06d818a04fd87dfeeb5
$ git checkout HEAD^
$ camlp4o -printer o -no_comments ocaml/xapi/import_raw_vdi.ml | md5sum
e74faa7367f4c06d818a04fd87dfeeb5

Signed-off-by: David Scott <dave.scott@eu.citrix.com>