soc/qman: test: Fix implementation of fd_cmp()

This function must only return the truth value of whether
two frame descriptors are different or not.
It does NOT have to compute some obscure difference between
fd fields and return it as an int, making sparse complain
about type conversions in the process.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Scott Wood <oss@buserror.net>