cli: Explicitly cast float to int, to silence MSVC warnings
This fixes these warnings:
tools/output/y4m2.c(82): warning C4244: 'initializing': conversion from 'double' to 'int', possible loss of data
tools/output/y4m2.c(83): warning C4244: 'initializing': conversion from 'double' to 'int', possible loss of data