crypto: qat - avoid division by zero

Check if delta_us is not zero and return -EINVAL if it is.
delta_us is unlikely to be zero as there is a sleep between the reads of
the two timestamps.

This is to fix the following warning when compiling the QAT driver
using clang scan-build:
    drivers/crypto/intel/qat/qat_common/adf_clock.c:87:9: warning: Division by zero [core.DivideZero]
       87 |         temp = DIV_ROUND_CLOSEST_ULL(temp, delta_us);
          |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: e2980ba5 ("crypto: qat - add measure clock frequency")
Signed-off-by: Adam Guerin <adam.guerin@intel.com>
Reviewed-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>