backport: Add an implementation of get_random_int() for <3.10 kernels.

backport: Add an implementation of get_random_int() for <3.10 kernels.

get_random_int() was present, but simply not exported for use in modules
until 3.10.  Implement it in terms of the more expensive get_random_bytes()

This is needed by the cw1200 driver.

Signed-off-by: Solomon Peachy <pizza@shaftnet.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>