avconv_opt: Add missing comma

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

avconv_opt.c

@@ -2445,7 +2445,7 @@ const OptionDef options[] = {
         "use HW accelerated decoding", "hwaccel name" },
     { "hwaccel_device",   OPT_VIDEO | OPT_STRING | HAS_ARG | OPT_EXPERT |
                           OPT_SPEC | OPT_INPUT,                                  { .off = OFFSET(hwaccel_devices) },
-        "select a device for HW acceleration" "devicename" },
+        "select a device for HW acceleration", "devicename" },
     { "autorotate",       HAS_ARG | OPT_BOOL | OPT_SPEC |
                           OPT_EXPERT | OPT_INPUT,                                { .off = OFFSET(autorotate) },
         "automatically insert correct rotate filters" },