gfio: set option category for create_only

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/options.c b/options.c
index 0074e5f..2201f59 100644
--- a/options.c
+++ b/options.c
@@ -2225,6 +2225,7 @@
 		.type	= FIO_OPT_BOOL,
 		.off1	= td_var_offset(create_only),
 		.help	= "Only perform file creation phase",
+		.category = FIO_OPT_C_FILE,
 		.def	= "0",
 	},
 	{