MAINT: fix gdr_unpin_buffer warning

* Fix the warning message when `gdr_unpin_buffer`
fails, so that the message is not conflated with
the prior `gdr_unmap` call.

Signed-off-by: Tyler Reddy <tyler.je.reddy@gmail.com>

src/hmem_cuda_gdrcopy.c

@@ -368,7 +368,7 @@ int cuda_gdrcopy_dev_unregister(uint64_t handle)
 	err = global_gdrcopy_ops.gdr_unpin_buffer(global_gdr, gdrcopy->mh);
 	if (err) {
 		FI_WARN(&core_prov, FI_LOG_MR,
-			"gdr_unmap failed! error: %s\n",
+			"gdr_unpin_buffer failed! error: %s\n",
 			strerror(err));
 		goto exit;
 	}