staging: r8188eu: use htons macro instead of __constant_htons

Macro "htons" is more efficient and clearer. It should be used for
constants instead of the __constant_htons macro. Resolves following
checkpatch script complaint:
        WARNING: __constant_htons should be htons

Signed-off-by: Deepak R Varma <drv@mailo.com>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/b46adfbdce0362ed0dbe0fc957ef2f47a93c24bb.1666299151.git.drv@mailo.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>