staging: wilc1000: Replaced comparison to NULL statements

This patch corrects checks generated by checkpatch.pl by
replacing comparison to null statements with equivalent
statements in the form "x" or "!x"

Signed-off-by: Roger H. Newell <newell.roger@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>