staging/lustre: use ktime_t for calculating elapsed time

process_param2_config() tries to print how much time has passed
across a call_usermodehelper() function, and uses struct timeval
for that.

We want to remove this structure, so this is better expressed
in terms of ktime_t and ktime_us_delta().

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>