lib: util: fix wrong string of string_of_va_chroma_format
The string_of_va_chroma_format get wrong string format description. For example, the YUV420_10BPP get a string of 0x00000100 as output. It's interesting because all the VA_RT_FORMAT_xxx values are macro definition. And the macro STRINGIFY(VA_RT_FORMAT_xxx) will expand VA_RT_FORMAT_xxx to its real value 0x00000XXX.