Dashplayer: fix writeString16
- writeString16 uses uint16 instead of char16
- fixes error: invalid conversion from 'char16_t*' to 'const uint16_t* on linaro-4.8 toolchain
Signed-off-by: Luis Cruz <ljc2491@gmail.com>

Change-Id: I1dcae9137e5c5b028b0de94b5c2f3f267d653f65