x86/percpu: Fix __per_cpu_hot_end marker

Make __per_cpu_hot_end marker point to the end of the percpu cache
hot data, not to the end of the percpu cache hot section.

This fixes CONFIG_MPENTIUM4 case where X86_L1_CACHE_SHIFT
is set to 7 (128 bytes).

Also update assert message accordingly.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Link: https://lore.kernel.org/r/20250304173455.89361-1-ubizjak@gmail.com

Closes: https://lore.kernel.org/lkml/Z8a-NVJs-pm5W-mG@gmail.com/