fifo8: replace fifo8_pop_bufptr() with fifo8_peekpop_bufptr() in fifo8_pop_buf()

fifo8: replace fifo8_pop_bufptr() with fifo8_peekpop_bufptr() in fifo8_pop_buf()

The upcoming peek functionality will require passing a non-zero
value to fifo8_peekpop_bufptr().

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Octavian Purdila <tavip@google.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240828122258.928947-5-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>