mwifiex: fix bug in wildcard scan handling

Currently if valid SSID list is provided in scan request, driver
performs specific SSID scan otherwise wildcard scan is chosen.

When wpa_supplicant provides valid SSID list followed by
zero-length SSID for wildcard scan, only specific SSID scan is
performed by driver. Actually driver is expected to do both type
of scanning in this case. The patch fixes this issue.

Also, use SSID list pointer provided by stack directly, instead
of copying SSID's to local structure.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>