crypto/NX: Set receive window credits to max number of CRBs in RxFIFO

System gets checkstop if RxFIFO overruns with more requests than the
maximum possible number of CRBs in FIFO at the same time. The max number
of requests per window is controlled by window credits. So find max
CRBs from FIFO size and set it to receive window credits.

Fixes: b0d6c9ba ("crypto/nx: Add P9 NX support for 842 compression engine")
CC: stable@vger.kernel.org # v4.14+
Signed-off-by: Haren Myneni <haren@us.ibm.com>

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>