[media] rtl2832_sdr: remove plain 64-bit divisions

Commit 0ba2aeb6
(v4l2-ctrls: increase internal min/max/step/def to 64 bit)
changes v4l2 controls to 64-bit. Driver it not working on 32-bit
arch as it uses directly control 'step' which is changed to 64-bit.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>