MdeModulePkg/EhciDxe: Fix legacy handoff logic #327

Job	Run time
Linux GCC AMD	14m 35s
Linux GCC AMD	15m 26s
Linux GCC Common	19m 12s
Linux GCC Common	18m 50s
Linux GCC ARM	11m 8s
Linux GCC ARM	10m 40s
Test ARM (ArmVirtQemu, ARM,AARCH64, GCC, RELEASE,DEBUG)	3m 0s
Test ARM (ArmVirtQemu, ARM,AARCH64, GCC, RELEASE,DEBUG)	3m 14s
Test AMD (Ovmf, Ia32,X64,3264, GCC, RELEASE,DEBUG)	5m 41s
Test AMD (Ovmf, Ia32,X64,3264, GCC, RELEASE,DEBUG)	6m 45s
	1h 48m 31s

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