net: dsa: seville: the packet buffer is 2 megabits, not megabytes

The VSC9953 Seville switch has 2 megabits of buffer split into 4360
words of 60 bytes each. 2048 * 1024 is 2 megabytes instead of 2 megabits.
2 megabits is (2048 / 8) * 1024 = 256 * 1024.

Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Fixes: a63ed92d

 ("net: dsa: seville: fix buffer size of the queue system")
Link: https://lore.kernel.org/r/20201019050625.21533-1-fido_max@inbox.ru
Signed-off-by: Jakub Kicinski <kuba@kernel.org>