printk_ringbuffer: don't needlessly wrap data blocks around

printk_ringbuffer: don't needlessly wrap data blocks around

Previously, data blocks that perfectly fit the data ring buffer would
get wrapped around to the beginning for no reason since the calculated
offset of the next data block would belong to the next wrap. Since this
offset is not actually part of the data block, but rather the offset of
where the next data block is going to start, there is no reason to
include it when deciding whether the current block fits the buffer.

Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Tested-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20250905144152.9137-2-d-tatianin@yandex-team.ru
[pmladek@suse.com: Updated indentation.]
Signed-off-by: Petr Mladek <pmladek@suse.com>