Add missing return statements which fix crashes in release mode.

Add flag to compiler so that it generates an error when a returning function does not return something...

cmake-nRF5x/CMake_nRF5x.cmake

@@ -88,7 +88,7 @@ macro(nRF5x_setup)
         set(SOFTDEVICE_PATH "${NRF5_SDK_PATH}/components/softdevice/s132/hex/s132_nrf52_6.1.1_softdevice.hex")
     endif ()
 
-    set(COMMON_FLAGS "-MP -MD -mthumb -mabi=aapcs -Wall -g3 -ffunction-sections -fdata-sections -fno-strict-aliasing -fno-builtin --short-enums ${CPU_FLAGS}")
+    set(COMMON_FLAGS "-MP -MD -mthumb -mabi=aapcs -Wall -g3 -ffunction-sections -fdata-sections -fno-strict-aliasing -fno-builtin --short-enums ${CPU_FLAGS} -Wreturn-type -Werror=return-type")
 
     # compiler/assambler/linker flags
     set(CMAKE_C_FLAGS "${COMMON_FLAGS}")

src/DisplayApp/DisplayApp.cpp

@@ -9,7 +9,7 @@ using namespace Pinetime::Applications;
 
 Pinetime::Drivers::st7789 lcd;
 ret_code_t lcd_init() {
-  lcd.Init();
+  return lcd.Init();
 }
 
 void lcd_dummy() {
@@ -38,7 +38,7 @@ static lcd_cb_t st7789_cb = {
         .width = 240
 };
 
-const nrf_lcd_t nrf_lcd_st7789 = {
+static const nrf_lcd_t nrf_lcd_st7789 = {
         .lcd_init = lcd_init,
         .lcd_uninit = lcd_dummy,
         .lcd_pixel_draw = lcd_pixel_draw,
@@ -64,7 +64,7 @@ void DisplayApp::Process(void *instance) {
   auto* app = static_cast<DisplayApp*>(instance);
 
   NRF_LOG_INFO("DisplayApp task started!");
-  gfx_initialization();
+  app->gfx_initialization();
   uint8_t hour = 0;
   uint8_t minute = 1;
   while (1) {

src/DisplayApp/DisplayApp.h

@@ -11,7 +11,7 @@ namespace Pinetime {
       private:
         TaskHandle_t taskHandle;
         static void Process(void* instance);
-        static void gfx_initialization();
+        void gfx_initialization();
 
     };
   }

src/drivers/st7789.cpp

@@ -8,7 +8,7 @@ using namespace Pinetime::Drivers;
 ret_code_t st7789::Init() {
   InitHw();
   InitCommands();
-
+  return 0;
 }
 
 ret_code_t st7789::InitHw() const {