staging: r8188eu: replace switch-case with if

Replace a switch-case in rtw_write_port with an if statement and make the
code a bit shorter.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20230130195303.138941-10-martin@kaiser.cx


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