ocxl: Fix return value check in afu_ioctl()

In case of error, the function eventfd_ctx_fdget() returns ERR_PTR() and
never returns NULL. The NULL test in the return value check should be
replaced with IS_ERR().

This issue was detected by using the Coccinelle software.

Fixes: 0601466 ("ocxl: move event_fd handling to frontend")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Alastair D'Silva <alastair@d-silva.org>
Acked-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/ocxl/file.c

@@ -257,8 +257,8 @@ static long afu_ioctl(struct file *file, unsigned int cmd,
 			return -EINVAL;
 		irq_id = ocxl_irq_offset_to_id(ctx, irq_fd.irq_offset);
 		ev_ctx = eventfd_ctx_fdget(irq_fd.eventfd);
-		if (!ev_ctx)
-			return -EFAULT;
+		if (IS_ERR(ev_ctx))
+			return PTR_ERR(ev_ctx);
 		rc = ocxl_irq_set_handler(ctx, irq_id, irq_handler, irq_free, ev_ctx);
 		break;