powerpc/powernv/idle: Fix build error

Fix the below build error using strlcpy instead of strncpy

In function 'pnv_parse_cpuidle_dt',
    inlined from 'pnv_init_idle_states' at arch/powerpc/platforms/powernv/idle.c:840:7,
    inlined from '__machine_initcall_powernv_pnv_init_idle_states' at arch/powerpc/platforms/powernv/idle.c:870:1:
arch/powerpc/platforms/powernv/idle.c:820:3: error: 'strncpy' specified bound 16 equals destination size [-Werror=stringop-truncation]
   strncpy(pnv_idle_states[i].name, temp_string[i],
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    PNV_IDLE_NAME_LEN);

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>