arm64: hibernate: remove WARN_ON in save_processor_state

arm64: hibernate: remove WARN_ON in save_processor_state

During hibernation or restoration, freeze_secondary_cpus
checks num_online_cpus via BUG_ON, and the subsequent
save_processor_state also does the checking with WARN_ON.

In the case of CONFIG_PM_SLEEP_SMP=n, freeze_secondary_cpus
is not defined, but the sole possible condition to disable
CONFIG_PM_SLEEP_SMP is !SMP where num_online_cpus is always 1.
We also don't have to check it in save_processor_state.

So remove the unnecessary checking in save_processor_state.

Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230609075049.2651723-3-songshuaishuai@tinylab.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>