ui: Clean up local variable shadowing

Local variables shadowing other local variables or parameters make the
code needlessly hard to understand.  Tracked down with -Wshadow=local.
Clean up: delete inner declarations when they are actually redundant,
else rename variables.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-ID: <20230921121312.1301864-4-armbru@redhat.com>

ui/vnc-palette.c

@@ -86,8 +86,6 @@ int palette_put(VncPalette *palette, uint32_t color)
         return 0;
     }
     if (!entry) {
-        VncPaletteEntry *entry;
-
         entry = &palette->pool[palette->size];
         entry->color = color;
         entry->idx = idx;