modetest: fix drmModeGetConnector memory leak

Don't "continue" without freeing the connector.

192 bytes in 6 blocks are indirectly lost in loss record 6 of 12
   at 0x4C2779D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x4E30DD8: drmMalloc (xf86drm.c:147)
   by 0x4E35024: drmAllocCpy (xf86drmMode.c:73)
   by 0x4E35D69: drmModeGetConnector (xf86drmMode.c:507)
   by 0x402F22: dump_connectors (modetest.c:181)
   by 0x40261B: main (modetest.c:801)

Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>