The do_gettimeofday() helper was removed by commit e4b92b108c6c
("timekeeping: remove obsolete time accessors") in v5.0-rc1 and commit
c766d1472c70 ("y2038: hide timeval/timespec/itimerval/itimerspec types")
in v5.6-rc3 hides struct timeval from kernel code.
Replace the use of do_gettimeofday() and struct timeval in linux/driver.c.
While ktime_get_real_ns() would match do_gettimeofday() better, monotonic
timer seems more appropriate for poll timeouts so use ktime_get_ns()
instead.