fifo8: introduce head variable for fifo8_peekpop_bufptr()

Rather than operate on fifo->head directly, introduce a new head
variable which is set to the value of fifo->head and use it instead.
This is to allow future adjustment of the head position within the
internal FIFO buffer.

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: <20240828122258.928947-3-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

util/fifo8.c

@@ -75,11 +75,12 @@ static const uint8_t *fifo8_peekpop_bufptr(Fifo8 *fifo, uint32_t max,
                                            uint32_t *numptr, bool do_pop)
 {
     uint8_t *ret;
-    uint32_t num;
+    uint32_t num, head;
 
     assert(max > 0 && max <= fifo->num);
-    num = MIN(fifo->capacity - fifo->head, max);
-    ret = &fifo->data[fifo->head];
+    head = fifo->head;
+    num = MIN(fifo->capacity - head, max);
+    ret = &fifo->data[head];
 
     if (do_pop) {
         fifo->head += num;