e1000e: Fix -Wformat-truncation warnings

e1000e: Fix -Wformat-truncation warnings

Provide precision hints to snprintf() since we know the destination
buffer size of the RX/TX ring names are IFNAMSIZ + 5 - 1. This fixes the
following warnings:

drivers/net/ethernet/intel/e1000e/netdev.c: In function
'e1000_request_msix':
drivers/net/ethernet/intel/e1000e/netdev.c:2109:13: warning: 'snprintf'
output may be truncated before the last format character
[-Wformat-truncation=]
     "%s-rx-0", netdev->name);
             ^
drivers/net/ethernet/intel/e1000e/netdev.c:2107:3: note: 'snprintf'
output between 6 and 21 bytes into a destination of size 20
   snprintf(adapter->rx_ring->name,
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     sizeof(adapter->rx_ring->name) - 1,
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     "%s-rx-0", netdev->name);
     ~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/intel/e1000e/netdev.c:2125:13: warning: 'snprintf'
output may be truncated before the last format character
[-Wformat-truncation=]
     "%s-tx-0", netdev->name);
             ^
drivers/net/ethernet/intel/e1000e/netdev.c:2123:3: note: 'snprintf'
output between 6 and 21 bytes into a destination of size 20
   snprintf(adapter->tx_ring->name,
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     sizeof(adapter->tx_ring->name) - 1,
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     "%s-tx-0", netdev->name);
     ~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>