cmd/compile/internal/sparc64: fix all type conversions
cmd/compile/internal/sparc64: fix all type conversions

convert.go now passes.

Change-Id: I8ca401ee4c55992e678d216a0f88c297ccffd8f3

4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go