staging: vt6655: Fix *Duration s_uFillDataHead to return to __le16

All callers should be __le16.

Fix vGenerateMACHeader duration to __le16 and reverse the endian
conversion.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>