staging: r8188eu: remove unnecessary type casts

The field rx_data of struct recv_frame and the local variable pframe
both have type (u8 *). Remove unnecessary type casts to (unsigned char *).

Acked-by: Phillip Potter <phil@philpotter.co.uk>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210829112555.8726-4-straube.linux@gmail.com


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