Fix Seg Fault error when reading in an RR Graph with different x-y segment types

[kimiatkh]

Description

The pull request is to fix the segmentation fault that occurred when reading in the rr graph that had different segment types in the X and Y directions. The error was caused by some parts of the code that set the node cost index, which still relied on the assumption that the X and Y axes have the same segment types. The issue has been fixed by updating the relevant code.

How Has This Been Tested?

The changes have been tested using the Stratix 10 architecture. Before the fix, the rr graph could not be read in properly, resulting in the segmentation fault. After applying the fix, the issue has been resolved, and the rr graph is now correctly processed without any errors.

Types of changes

• Bug fix (change which fixes an issue)
• New feature (change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

[vaughnbetz]

Looks good, thanks.