target/ppc: init 'sregs' in kvmppc_put_books_sregs()

target/ppc: init 'sregs' in kvmppc_put_books_sregs()

Init 'sregs' to avoid Valgrind complaints about uninitialized bytes
from kvmppc_put_books_sregs():

==54059== Thread 3:
==54059== Syscall param ioctl(generic) points to uninitialised byte(s)
==54059==    at 0x55864E4: ioctl (in /usr/lib64/libc.so.6)
==54059==    by 0xD1FA23: kvm_vcpu_ioctl (kvm-all.c:3053)
==54059==    by 0xAFB18B: kvmppc_put_books_sregs (kvm.c:891)
==54059==    by 0xAFB47B: kvm_arch_put_registers (kvm.c:949)
==54059==    by 0xD1EDA7: do_kvm_cpu_synchronize_post_init (kvm-all.c:2766)
==54059==    by 0x481AF3: process_queued_cpu_work (cpus-common.c:343)
==54059==    by 0x4EF247: qemu_wait_io_event_common (cpus.c:412)
==54059==    by 0x4EF343: qemu_wait_io_event (cpus.c:436)
==54059==    by 0xD21E83: kvm_vcpu_thread_fn (kvm-accel-ops.c:54)
==54059==    by 0xFFEBF3: qemu_thread_start (qemu-thread-posix.c:556)
==54059==    by 0x54E6DC3: start_thread (in /usr/lib64/libc.so.6)
==54059==    by 0x5596C9F: clone (in /usr/lib64/libc.so.6)
==54059==  Address 0x799d1cc is on thread 3's stack
==54059==  in frame #2, created by kvmppc_put_books_sregs (kvm.c:851)
==54059==  Uninitialised value was created by a stack allocation
==54059==    at 0xAFAEB0: kvmppc_put_books_sregs (kvm.c:851)

This happens because Valgrind does not consider the 'sregs'
initialization done by kvm_vcpu_ioctl() at the end of the function.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220331001717.616938-4-danielhb413@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>