staging: wilc1000: rename variable gu32FlushedJoinReqSize

This patch renames variable gu32FlushedJoinReqSize to join_req_size
to avoid CamelCase naming convention.

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