drm/msm/gem: Add check for kmalloc

Add the check for the return value of kmalloc in order to avoid
NULL pointer dereference in copy_from_user.

Fixes: 20224d71

 ("drm/msm/submit: Move copy_from_user ahead of locking bos")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/514678/
Link: https://lore.kernel.org/r/20221212091117.43511-1-jiasheng@iscas.ac.cn
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>