lv2: fix build without the debug system
FAILED: subprojects/gst-plugins-bad/ext/lv2/b8a2ebe@@gstlv2@sha/gstlv2utils.c.o
../subprojects/gst-plugins-bad/ext/lv2/gstlv2utils.c: In function 'lv2_log_printf':
../subprojects/gst-plugins-bad/ext/lv2/gstlv2utils.c:50:3: error: attempt to use poisoned "gst_debug_log_valist"
50 | gst_debug_log_valist (lv2_debug, GST_LEVEL_INFO, "", "", 0, NULL, fmt, ap);
| ^
../subprojects/gst-plugins-bad/ext/lv2/gstlv2utils.c:50:25: error: 'lv2_debug' undeclared (first use in this function); did you mean 'g_debug'?
50 | gst_debug_log_valist (lv2_debug, GST_LEVEL_INFO, "", "", 0, NULL, fmt, ap);
| ^~~~~~~~~
| g_debug