Fix TIM6_IRQn definition

If no DAC then TIM6_IRQn is already defined.
Fixes #739

Signed-off-by: Frederic Pillon <[email protected]>

Author: fpistm

Diff for: cores/arduino/stm32/timer.h

@@ -59,6 +59,7 @@ extern "C" {
 #endif
 #endif
 #if defined(TIM6_BASE) && !defined(TIM6_IRQn)
+#if defined(DAC_BASE) || defined(DAC1_BASE)
 #if defined(STM32G0xx)
 #define TIM6_IRQn TIM6_DAC_LPTIM1_IRQn
 #define TIM6_IRQHandler TIM6_DAC_LPTIM1_IRQHandler
@@ -67,6 +68,7 @@ extern "C" {
 #define TIM6_IRQHandler TIM6_DAC_IRQHandler
 #endif
 #endif
+#endif
 #if defined(TIM7_BASE) && !defined(TIM7_IRQn)
 #if defined(STM32G0xx)
 #define TIM7_IRQn TIM7_LPTIM2_IRQn