feat(mt8188): update return value in mtk_emi_mpu_sip_handler

Remove the use of SMC_RET2 in the mtk_emi_mpu_sip_handler function. The
current smc driver in the atf driver has switched to using SMC_RET4 for
smc call clients. This change aligns the return value handling with the
updated driver behavior that ensures consistency and avoids potential
issues with the old return value.

Change-Id: I87f25b438d2119837c45bed80a8224fcfd141fb6
1 file changed