m7ul: HTC not htc

Replace htc with HTC in full_m7ul.mk. HTC stylizes their name in uppercase.
Additionally, this make the device name look cleaner in the Play Store, as
well as in Android Device Manager and other places that use these settings
to identify the device manufacturer.

Change-Id: I8014c34e897a2b4e8394e767b9ff8cfadcd665b5