bfin: do not reset dispatch needed

Closes #2148

Fix suggested in above ticket. On examination, the assembly
appears to be clearing the DISPATCH_NEEDED flag before jumping
to _Thread_Dispatch.

cpukit/score/cpu/bfin/cpu_asm.S

@@ -472,8 +472,6 @@ noStackRestore:
 	cc = r0 == 0;
 	if cc jump noDispatch
 doDispatch:
-	r0 = 0;
-	B[p0] = r0;
 	raise 15;
 noDispatch:
 	r0 = [sp++];