drivers: soc: qcom: Use number of bytes returned from PRNG for entropy

Use the number of bytes returned from the PRNG to specify the amount of
entropy that we are contributing to the random pool instead of assuming
we receive the amount requested.

Change-Id: I5d49206146fd5f18f69516e4ba31dd3a38a81d62
[ohaugan@codeaurora.org: Fixed trivial merge conflicts]
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>