V4L/DVB (11898): cx18: Perform 64 bit divide so it works for 32 bit systems

Thanks to David Ward and Mike Krufky for reporting the problem and
debugging this as an unresolved symbol due to a 64 bit divide on a 32 bit
system.  David Ward provided the content of this patch; Andy Walls only
performed some cosmetic edits.

Reported-by: David Ward <david.ward@gatech.edu>
Signed-off-by: David Ward <david.ward@gatech.edu>
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>