nouveau/dmem: Remove duplicated include in nouveau_dmem.c

./drivers/gpu/drm/nouveau/nouveau_dmem.c: nvif/if000c.h is included more
than once.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2404


Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221017000723.113744-1-yang.lee@linux.alibaba.com