staging: r8192e_pci: fix htons error

A sparse error fixup removed a htons() which is required for the driver
to function. This patch puts the htons() back and fixes the sparse
warning correctly by changing the left side cast.

Signed-off-by: Sean MacLennan <seanm@seanm.ca>
Cc: stable <stable@vger.kernel.org> # 3.14
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>