Staging: wlan-ng: Fix endian error

sparse report fixed:
drivers/staging//wlan-ng//hfa384x_usb.c:3517:35: warning: restricted __be64 degrades to integer
drivers/staging//wlan-ng//hfa384x_usb.c:3517:33: warning: incorrect type in assignment (different base types)
drivers/staging//wlan-ng//hfa384x_usb.c:3517:33:    expected restricted __be64 [usertype] mactime
drivers/staging//wlan-ng//hfa384x_usb.c:3517:33:    got unsigned long long

Computation on the value should be done when in machine format, not in big endian format.

Signed-off-by: Adrien Descamps <adrien.descamps@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>