drm/nouveau/bios: fix DCB v1.5 parsing

memcmp->nv_strncmp conversion, in addition to name change, should have
inverted the return value.

But nv_strncmp does not act like strncmp - it does not check for string
terminator, returns true/false instead of -1/0/1 and has different
parameters order.

Let's rename it to nv_memcmp and let it act like memcmp.

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>