usb: xhci: tegra: use time64_t for printing timestamp

The time_t type and time_to_tm() function are deprecated because
of y2038 problems. In this driver, they are used to pretty-print
the timestamp of the firmware build. This is fine as long as
we don't get a firmware build past 2038.

Converting to time64_t and time64_to_tm() avoids the deprecated
interfaces and works until 2106, when the firmware-defined
data structure overflows.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>