staging: bcm2835-camera use ktime_t for timestamps

commit 6cf83f2a upstream with
minor mods

struct timeval is deprecated for in-kernel use, and converting
this function to use ktime_t makes it simpler as well.

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