staging: wilc1000: remove pointless kfree wrapper

It isn't needed, and we were checking if a buffer was not NULL multiple
times, no one had ever looked at the code :(

Cc: Johnny Kim <johnny.kim@atmel.com>
Cc: Rachel Kim <rachel.kim@atmel.com>
Cc: Dean Lee <dean.lee@atmel.com>
Cc: Chris Park <chris.park@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>