iop-adma: redundant/wrong tests in iop_*_count()?

When we reach the loop, len is at least 1, we only stay in the loop when
len is at least MAX_BYTE_COUNT + 1, MAX_BYTE_COUNT is subtracted in each
iteration. So when we leave the loop, or didn't take it, len is at least 1.
Testing whether len is non-zero appears redundant.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>