Fix Bug - CSR_DONE be cleared to write the MAJORELINK or ESG bits

Page 982.
Fixes https://forum.pjrc.com/threads/54711-Teensy-4-0-First-Beta-Test?p=196233&viewfull=1#post196233
- maybe this is needed for T3x, too? too late here to check this now.

teensy4/DMAChannel.h

@@ -374,6 +374,7 @@ protected:
 	DMABaseClass() {}
 
 	static inline void copy_tcd(TCD_t *dst, const TCD_t *src) {
+		dst->CSR &= ~DMA_TCD_CSR_DONE;
 		const uint32_t *p = (const uint32_t *)src;
 		uint32_t *q = (uint32_t *)dst;
 		uint32_t t1, t2, t3, t4;