Fix missing header after make install

[ddassie-texa]

Pull request

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• bug
• feature

Describe the pull request

This PR fixes the erpc_c Makefile, the erpc_simple_server.hpp header was never installed.

To Reproduce

Compile the library with make, than try to install it with make install, the erpc_simple_server.hpp file won't be copied to the include directory.

Expected behavior

erpc_simple_server.hpp should be installed and available to consumers.

Desktop (please complete the following information):

• OS: Linux Ubuntu 24.04 x86_64, Linux Yocto (multiple architectures)
• eRPC Version: v1.13.0

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