Staging: silicom: Remove unnecessary variable from do_cmd()

Remove unnecessary variable ioctl from do_cmd().

As a consequence, this patch removes an assignment to ioctl in an if condition,
reported by checkpatch.pl.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>