hwrng: Pass entropy to add_hwgenerator_randomness() in bits, not bytes

The entropy argument to add_hwgenerator_randomness() is passed
directly to credit_entropy_bits() so we should be passing the
number of bits, not bytes.

Change-Id: I068c1073245944dddf0cbf7e69f1c0f1d96010e2
Fixes: 646d838eef81 "hwrng: create filler thread"
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>