hw/ppc/spapr_drc.c: use g_auto in spapr_dt_drc()

hw/ppc/spapr_drc.c: use g_auto in spapr_dt_drc()

Use g_autoptr() with GArray* and GString* pointers to avoid calling
g_free() and the need for the 'out' label.

'drc_name' can also be g_autofreed to avoid a g_free() call at the end
of the while() loop.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220228175004.8862-7-danielhb413@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>