losetup: fix --direct-io

losetup: fix --direct-io

losetup checks for empty lo_flags when A_CREATE (action) is not
requested, otherwise it prints

	"the options %s are allowed during loop device setup only"

error message. We need to cleanup lo_flags when alone --direct-io
requested.

Fix also typo in man page, "losetup --direct-io" is the same as
"losetup --direct-io=on".

Signed-off-by: Karel Zak <kzak@redhat.com>