staging: comedi: avoid using timeval

Comedi uses 32-bit seconds for its timestamps, on both 32-bit and
64-bit machines. For all I can tell, this was originally meant as
a 'timespec', which would overflow in 2038 because of the use of
a signed 'long' on 32-bit machines, but it is now used as an
array of two unsigned 'lsampl_t' values in comedilib, which will
only overflow in 2106, on both 32-bit and 64-bit machines.

In an effort to get rid of all uses of 'struct timeval' in the kernel,
this replaces the internal code with a call to ktime_get_real_ts64()
and a comment at the location of the conversion.

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