[SPIRV] Audit select Result in SPIRVInstructionSelector (#115193)

- as per the definition of `select` in GlobalISel/InstructionSelector.h
the return value is a boolean denoting if the select was successful
- doing `Result |=` is incorrect as all inserted instructions should be
succesful, hence we change to using `Result &=`
- ensure that the return value of all BuildMI instructions are
propagated correctly

Author: inbelic