staging: rtl8188eu: convert variables from unsigned char to u8

Convert the local variables max_ampdu_len and min_mpdu_spacing from
unsigned char to u8 and remove unnecessary castings to u8 pointer.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20191015154535.27979-2-straube.linux@gmail.com


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