ras-events: quit loop in read_ras_event when kbuf data is broken

ras-events: quit loop in read_ras_event when kbuf data is broken

when kbuf data is broken, kbuffer_next_event() may move kbuf->index back to
the current kbuf->index position, causing dead loop.

In this situation, rasdaemon will repeatedly parse an invalid event, and
print warning like "ug! negative record size -8!", pushing cpu utilization
rate to 100%.

when kbuf data is broken, discard current page and continue reading next page
kbuf.

Signed-off-by: hubin <hubin73@huawei.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>