staging: wilc1000: use the real data type

This patch changes the type of gu8FlushedJoinReqDrvHandler with his real
data type becasue typecasting is not necessary. In result, typecasting
which is not necessary and some building warnings is removed.

Signed-off-by: Johnny Kim <johnny.kim@atmel.com>
Signed-off-by: Tony Cho <tony.cho@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>