libaio: fix double setting of option category

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/engines/libaio.c b/engines/libaio.c
index be54dca..9cc910d 100644
--- a/engines/libaio.c
+++ b/engines/libaio.c
@@ -34,7 +34,7 @@
 		.off1	= offsetof(struct libaio_options, userspace_reap),
 		.help	= "Use alternative user-space reap implementation",
 		.category = FIO_OPT_C_ENGINE,
-		.category = FIO_OPT_G_LIBAIO,
+		.group	= FIO_OPT_G_LIBAIO,
 	},
 	{
 		.name	= NULL,