net: dsa: mv88e6xxx: Prevent truncation of longer interrupt names

When adding support for unique interrupt names, after testing on a few
devices, it was assumed 32 characters would be sufficient. This
assumption turned out to be incorrect, ZII RDU2 for example uses a
device base name of mv88e6xxx-30be0000.ethernet-1:0, leaving no space
for post fixes such as -g1-atu-prob and -watchdog. The names then
become identical, defeating the point of the patch.

Increase the length of the string to 64 charactoes.

Reported-by: Chris Healy <Chris.Healy@zii.aero>
Fixes: 3095383a ("net: dsa: mv88e6xxx: Unique IRQ name")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>