mlir: Bugfixes with scf.for derivative #9422

Job	Run time
Enzyme CI LLVM 15 Debug macOS	5m 54s
Enzyme CI LLVM 15 Release macOS	4m 10s
Enzyme CI LLVM 15 Release ubuntu-22.04	4m 51s
Enzyme CI LLVM 16 Debug ubuntu-22.04	3m 56s
Enzyme CI LLVM 16 Release macOS	6m 35s
Enzyme CI LLVM 15 Debug ubuntu-22.04	4m 1s
Enzyme CI LLVM 16 Debug macOS	5m 23s
Enzyme CI LLVM 16 Release ubuntu-22.04	4m 30s
Enzyme CI LLVM 16 Release macOS XCode	3m 44s
	43m 4s

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