staging: csr: fix compilation warning in unifi_siwscan

got the warnings

drivers/staging/csr/sme_wext.c: In function ‘unifi_siwscan’:
drivers/staging/csr/sme_wext.c:1276:9: warning: variable ‘scantype’ set but not used [-Wunused-but-set-variable]

fixed by removing the variable

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>