nfp: fix simple vNIC mailbox length

The simple vNIC mailbox length should be 12 decimal and not 0x12.
Using a decimal also makes it clear this is a length value and not
another field within the simple mailbox defines.

Found by code inspection, there are no known firmware configurations
where this would cause issues.

Fixes: 527d7d1b ("nfp: read mailbox address from TLV caps")
Signed-off-by: NDirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfp_net_ctrl.h

@@ -392,7 +392,7 @@
 #define NFP_NET_CFG_MBOX_SIMPLE_CMD	0x0
 #define NFP_NET_CFG_MBOX_SIMPLE_RET	0x4
 #define NFP_NET_CFG_MBOX_SIMPLE_VAL	0x8
-#define NFP_NET_CFG_MBOX_SIMPLE_LEN	0x12
+#define NFP_NET_CFG_MBOX_SIMPLE_LEN	12
 
 #define NFP_NET_CFG_MBOX_CMD_CTAG_FILTER_ADD 1
 #define NFP_NET_CFG_MBOX_CMD_CTAG_FILTER_KILL 2