hwrng: Kconfig - Correct help text about feeding entropy pool

Modify Kconfig help text to reflect the fact that random data from hwrng
is fed into kernel random number generator's entropy pool.

Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>