target/ppc: initialize 'val' union in kvm_get_one_spr()

target/ppc: initialize 'val' union in kvm_get_one_spr()

Valgrind isn't convinced that we are initializing the values we assign
to env->spr[spr] because it doesn't understand that the 'val' union is
being written by the kvm_vcpu_ioctl() that follows (via struct
kvm_one_reg).

This results in Valgrind complaining about uninitialized values every
time we use env->spr in a conditional, like this instance:

==707578== Thread 1:
==707578== Conditional jump or move depends on uninitialised value(s)
==707578==    at 0xA10A40: hreg_compute_hflags_value (helper_regs.c:106)
==707578==    by 0xA10C9F: hreg_compute_hflags (helper_regs.c:173)
==707578==    by 0xA110F7: hreg_store_msr (helper_regs.c:262)
==707578==    by 0xA051A3: ppc_cpu_reset (cpu_init.c:7168)
==707578==    by 0xD4730F: device_transitional_reset (qdev.c:799)
==707578==    by 0xD4A11B: resettable_phase_hold (resettable.c:182)
==707578==    by 0xD49A77: resettable_assert_reset (resettable.c:60)
==707578==    by 0xD4994B: resettable_reset (resettable.c:45)
==707578==    by 0xD458BB: device_cold_reset (qdev.c:296)
==707578==    by 0x48FBC7: cpu_reset (cpu-common.c:114)
==707578==    by 0x97B5EB: spapr_reset_vcpu (spapr_cpu_core.c:38)
==707578==    by 0x97BABB: spapr_cpu_core_reset (spapr_cpu_core.c:209)
==707578==  Uninitialised value was created by a stack allocation
==707578==    at 0xB11F08: kvm_get_one_spr (kvm.c:543)

Initializing 'val' has no impact in the logic and makes Valgrind output
more bearable.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20220331001717.616938-2-danielhb413@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>