ppc: qtest already exports qtest_rtas_call()

ppc: qtest already exports qtest_rtas_call()

Having two functions with the same name is a bad idea.  As spapr only
uses the function locally, made it static.

When you compile with clang, you get this compilation error:

/usr/bin/ld: tests/qtest/libqos/libqos.fa.p/.._libqtest.c.o: in function `qtest_rtas_call':
/scratch/qemu/clang/full/all/../../../../../mnt/code/qemu/full/tests/qtest/libqtest.c:1195: multiple definition of `qtest_rtas_call'; libqemu-ppc64-softmmu.fa.p/hw_ppc_spapr_rtas.c.o:/scratch/qemu/clang/full/all/../../../../../mnt/code/qemu/full/hw/ppc/spapr_rtas.c:536: first defined here
clang-16: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
make: *** [Makefile:162: run-ninja] Error 1

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-ID: <20231030163834.4638-1-quintela@redhat.com>
[dhb: remove 'spapr_rtas.h' include from spapr_rtas.c]
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>