drm/radeon/benchmark: make sure bo blit copy exists before using it
drm/radeon/benchmark: make sure bo blit copy exists before using it

Fixes a segfault on asics without a blit callback.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=62239

Reviewed-by: Michel Dänzer <242b79f0804cf52679d58f27ed754158c1323c75@amd.com>
Signed-off-by: Alex Deucher <08dc22c6156113f2deff178e35e3ed9b24d6af9e@amd.com>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas