staging: rtlwifi: rtlwifi: use ktime_get_real_seconds() for suspend time

do_gettimeofday() is deprecated and slower than necessary for the purpose
of reading the seconds. This changes rtl_op_suspend/resume to use
ktime_get_real_seconds() instead, which is simpler and avoids confusion
about whether it is y2038-safe or not.

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