net: dsa: sja1105: Use units.h instead of the copy of a definition

BYTES_PER_KBIT is defined in units.h, use that definition.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20231128175027.394754-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>