mesa: fix _mesa_error() compiler warnings in shaderapi.c

mesa: fix _mesa_error() compiler warnings in shaderapi.c

Fix many instances of:
main/shaderapi.c: In function '_mesa_GetSubroutineUniformLocation':
main/shaderapi.c:2176:7: warning: format not a string literal and no format arguments [-Wformat-security]
       _mesa_error(ctx, GL_INVALID_OPERATION, api_name);
       ^

Ideally, many of these error messages should be improved to indicate
which argument is incorrect as we do in other parts of Mesa.

Reviewed-by: Kai Wasserbäch <kai@dev.carbon-project.org>
Tested-by: Kai Wasserbäch <kai@dev.carbon-project.org>