When port mirroring is added to a port, the bit position of the source
port, needs to be written to the register ANA_AC_PROBE_PORT_CFG.  This
register is replicated for n_ports > 32, and therefore we need to derive
the correct register from the port number.

Before this patch, we wrongly calculate the register from portno /
BITS_PER_BYTE, where the divisor ought to be 32, causing any port >=8 to
be written to the wrong register. We fix this, by using do_div(), where
the dividend is the register, the remainder is the bit position and the
divisor is now 32.

Fixes: 4e50d72b ("net: sparx5: add port mirroring implementation")
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241009-mirroring-fix-v1-1-9ec962301989@microchip.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>