kfifo: introduce and use kfifo_skip_count()

kfifo: introduce and use kfifo_skip_count()

kfifo_skip_count() is an extended version of kfifo_skip(), accepting
also count. This will be useful in the serial code later.

Now, it can be used to implement both kfifo_skip() and
kfifo_dma_out_finish(). In the latter, 'len' only needs to be divided by
'type' size (as it was until now).

And stop using statement expressions when the return value is cast to
'void'. Use classic 'do {} while (0)' instead.

Note: perhaps we should skip 'count' records for the 'recsize' case, but
the original (kfifo_dma_out_finish()) used to skip only one record. So
this is kept unchanged and 'count' is still ignored in the recsize case.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Stefani Seibold <stefani@seibold.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/r/20240405060826.2521-3-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>