Fix modelsim makefile space vs tab issue

What this MR does / why we need it:

Building the Modelsim platform fails to build with an error in a Makefile.

Error is:

makefile:41: *** missing separator.  Stop

This appears to have been introduced in 6190170b with a tab in the projects/core/hdl/platforms/modelsim/Makefile being erroneously replaced by spaces.

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Release Notes

N/A

Changelog

• bug(platforms): fix modelsim platform makefile space vs tab issue

Which issue(s) this MR closes

N/A