ocf-linux: tweak kernel patch for newer kernels

Newer kernels had a slight change in the random number API so the OCF
patchset requires a slight tweak to build and run properly.

Affected kernels are, per series:
>=3.0.41, >=3.2.29, >=3.4.9, >=3.5.2 and any newer version.

The fix is applied by detecting the API change rather than guessing the
kernel version.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>