Fix a typo in ISDBT Frontend.

FrontendIsdbtCoderate and FrontendIsdbtGuardInterval are typedefs in
HIDL HAL. The hidl2aidl tool used the original types in the parcelable
while conversion. And the wrong comment on FrontendIsdbtCoderate was
herited from HIDL too.

Bug: 191825295
Test: atest VtsHalTvTunerTargetTest
Change-Id: I44679e171b353010e9ea9cdd84b09a715459b4e7