Use kvmemdup instead of kvmalloc() + memcpy() to simplify the code.

No functional change intended.
Signed-off-by: Li Zetao <lizetao1@huawei.com>
Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/609596/Signed-off-by: Rob Clark <robdclark@chromium.org>