[mlir][Affine][NFC] Improve FlatAffineValueConstraint dump

Improve indentation for better readability.

Before:
```
Domain: 0, Range: 2, Symbols: 2, Locals: 1
5 constraints
(None	Value	Value	Value	Local	const)
1 1 0 -1 0 0 = 0
0 1 -1 0 0 0 >= 0
0 0 1 -1 2 2 >= 0
0 0 -1 1 -2 -1 >= 0
0 -1 1 0 2 0 >= 0
```

After:
```
Domain: 0, Range: 2, Symbols: 2, Locals: 1
5 constraints
(None	Value	Value	Value	Local	const)
 1	1	0	-1	0	0	= 0
 0	1	-1	0	0	0	>= 0
 0	0	1	-1	2	2	>= 0
 0	0	-1	1	-2	-1	>= 0
 0	-1	1	0	2	0	>= 0
```

Differential Revision: https://reviews.llvm.org/D144854