ea_malloc: Fix `defrag_free_list` block size bug. #1076

Job	Run time
compile-examples (arduino:mbed:nano33ble)	7m 58s
compile-examples (arduino:mbed:envie_m7)	16m 18s
compile-examples (arduino:mbed:nanorp2040connect)	12m 52s
compile-examples (arduino:mbed:nicla_sense)	7m 40s
compile-examples (arduino:mbed:nicla_vision)	11m 50s
compile-examples (arduino:mbed:opta)	15m 48s
compile-examples (arduino:mbed:giga)	24m 3s
compile-examples (arduino:mbed:nicla_voice)	5m 52s
compile-examples (arduino:mbed:edge_control)	5m 56s
compile-examples (arduino:mbed:envie_m7:target_core=cm4, - libraries/KernelDebug - libraries/Port...	4m 48s
	1h 53m 5s

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