staging: wilc1000: remove ununsed variable and associated line

This patch removes a unused variable 'u16RespLen' that is assigned a
value that is never used. The line that does the assignment is also
removed.

Signed-off-by: Hari Prasath Gujulan Elango <hgujulan@visteon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>