powerpc/vas: Fix potential NULL pointer dereference

(!ptr && !ptr->foo) strikes again. :)

The expression (!ptr && !ptr->foo) is bogus and in case ptr is NULL,
it leads to a NULL pointer dereference: ptr->foo.

Fix this by converting && to ||

This issue was detected with the help of Coccinelle, and audited and
fixed manually.

Fixes: 1a0d0d5e ("powerpc/vas: Add platform specific user window operations")
Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211015050345.GA1161918@embeddedor

arch/powerpc/platforms/book3s/vas-api.c

@@ -303,7 +303,7 @@ static int coproc_ioc_tx_win_open(struct file *fp, unsigned long arg)
 		return -EINVAL;
 	}
 
-	if (!cp_inst->coproc->vops && !cp_inst->coproc->vops->open_win) {
+	if (!cp_inst->coproc->vops || !cp_inst->coproc->vops->open_win) {
 		pr_err("VAS API is not registered\n");
 		return -EACCES;
 	}
@@ -373,7 +373,7 @@ static int coproc_mmap(struct file *fp, struct vm_area_struct *vma)
 		return -EINVAL;
 	}
 
-	if (!cp_inst->coproc->vops && !cp_inst->coproc->vops->paste_addr) {
+	if (!cp_inst->coproc->vops || !cp_inst->coproc->vops->paste_addr) {
 		pr_err("%s(): VAS API is not registered\n", __func__);
 		return -EACCES;
 	}