Fix cppcheck redundantAssignment for OLED_GEOMETRY_OVERRIDE variants (#11325)

`pio check` reports at src/main.cpp:878:

  [low:style] Variable 'screen_geometry' is reassigned a value before the
  old one has been used. [redundantAssignment]

for every variant that pins its panel size with OLED_GEOMETRY_OVERRIDE
(t-impulse-plus -> GEOMETRY_64_32, t-echo-card -> GEOMETRY_72_40). The
diagnostic pairs the override write with the `GEOMETRY_128_128` write in
the SH1107 normalization branch: on those boards that write is a dead
store, clobbered a few lines later.

Skip the geometry writes when the variant pins the panel size. The
screen_model normalization still runs (the driver needs it) and
precedence is unchanged - the override still wins on those boards, and
nothing changes for boards without one. The compile-time USE_SH1107
write is guarded the same way so the defect can't reappear if a future
variant combines the two.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

src/main.cpp

@@ -878,9 +878,13 @@ void setup()
 
 #if HAS_SCREEN
         // fixed screen override?
+        // The geometry picks below are skipped on variants that pin the panel size with
+        // OLED_GEOMETRY_OVERRIDE (see the end of this block) - there they would only be dead stores.
 #if defined(USE_SH1107)
     screen_model = meshtastic_Config_DisplayConfig_OledType_OLED_SH1107; // set dimension of 128x128
+#ifndef OLED_GEOMETRY_OVERRIDE
     screen_geometry = GEOMETRY_128_128;
+#endif
 #elif defined(USE_SH1107_128_64)
     screen_model = meshtastic_Config_DisplayConfig_OledType_OLED_SH1107; // keep dimension of 128x64
 #else
@@ -889,7 +893,9 @@ void setup()
 
         // Fix: update geometry for SH1107 128x128 selected via menu
         if (screen_model == meshtastic_Config_DisplayConfig_OledType_OLED_SH1107_128_128) {
+#ifndef OLED_GEOMETRY_OVERRIDE
             screen_geometry = GEOMETRY_128_128;
+#endif
             screen_model = meshtastic_Config_DisplayConfig_OledType_OLED_SH1107; // normalize
         }
     }