drm/gma500: fix double free of gma_connector

clang static analysis reports this problem:

cdv_intel_dp.c:2101:2: warning: Attempt to free released memory
        kfree(gma_connector);
        ^~~~~~~~~~~~~~~~~~~~

In cdv_intel_dp_init() when the call to cdv_intel_edp_panel_vdd_off()
fails, the handler calls cdv_intel_dp_destroy(connector) which does
the first free of gma_connector. So adjust the goto label and skip
the second free.

Fixes: d112a816 ("gma500/cdv: Add eDP support")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201003193928.18869-1-trix@redhat.com