core: silence MSVC compiler warning
core: silence MSVC compiler warning

The return type of wcore_attrib_list_length() is int32_t and at the same
time MSVC promotes the (int32_t) math at the return line to int64_t thus
causing a warning message. Explicitly cast it to make MSVC happy.

Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>
Reviewed-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@linux.intel.com>

fjhenigman/waffle,maurossi/waffle,waffle-gl/waffle,fjhenigman/waffle,fjhenigman/waffle,waffle-gl/waffle,dcbaker/waffle,evelikov/waffle,dcbaker/waffle,waffle-gl/waffle,waffle-gl/waffle,dcbaker/waffle,maurossi/waffle,chadversary/waffle,maurossi/waffle,chadversary/waffle,evelikov/waffle,chadversary/waffle,evelikov/waffle