soc: apple: rtkit: Make shmem_destroy optional

shmem_destroy isn't always required for coprocessor-managed buffers but we
still enforce that it exists. Just relax the check.

Reviewed-by: Alyssa Rosenzweig <[e-mail]>
Reviewed-by: Neal Gompa <[e-mail]>
Signed-off-by: Sven Peter <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/soc/apple/rtkit.c

···
 	dev_dbg(rtk->dev, "RTKit: buffer request for 0x%zx bytes at %pad\n",
 		buffer->size, &buffer->iova);
 
-	if (buffer->iova &&
-	    (!rtk->ops->shmem_setup || !rtk->ops->shmem_destroy)) {
+	if (buffer->iova && !rtk->ops->shmem_setup) {
 		err = -EINVAL;
 		goto error;
 	}