drm/nouveau/acr: Fix undefined behavior in nvkm_acr_hsfw_load_bl()

In nvkm_acr_hsfw_load_bl(), the return value of kmalloc() is directly
passed to memcpy(), which could lead to undefined behavior on failure
of kmalloc().

Fix this bug by using kmemdup() instead of kmalloc()+memcpy().

This bug was found by a static analyzer.

Builds with 'make allyesconfig' show no new warnings,
and our static analyzer no longer warns about this code.

Fixes: 22dcda45 ("drm/nouveau/acr: implement new subdev to replace "secure boot"")
Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220124165856.57022-1-zhou1615@umn.edu