[MLIR] Fix AsmPrinter.cpp for single ssa-id AffineMap
The AsmPrinter wrongly assumes that all single ssa-id AffineMap
are the identity map for the purpose of printing.
This CL adds the missing level of indirection as well as a test.
This bug was originally shaken off by the experimental TC->MLIR path.
Before this CL, the test would print:
```
mlfunc @mlfuncsimplemap(%arg0 : affineint, %arg1 : affineint, %arg2 : affineint) {
for %i0 = 0 to %arg0 {
for %i1 = 0 to %i0 {
~~~ should be %arg1
%c42_i32 = constant 42 : i32
}
}
return
}
```
PiperOrigin-RevId: 214120817
2 files changed
