sgi-xp: make some symbols static in xpnet.c

Fix the following sparse warning:

drivers/misc/sgi-xp/xpnet.c:99:19: warning: symbol 'xpnet_device' was
not declared. Should it be static?
drivers/misc/sgi-xp/xpnet.c:134:22: warning: symbol 'xpnet_dbg_name' was
not declared. Should it be static?
drivers/misc/sgi-xp/xpnet.c:138:15: warning: symbol 'xpnet_dbg_subname'
was not declared. Should it be static?
drivers/misc/sgi-xp/xpnet.c:143:15: warning: symbol 'xpnet' was not
declared. Should it be static?

Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Jason Yan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/sgi-xp/xpnet.c

···
 	atomic_t use_count;
 };
 
-struct net_device *xpnet_device;
+static struct net_device *xpnet_device;
 
 /*
  * When we are notified of other partitions activating, we add them to
···
 
 /* Define the XPNET debug device structures to be used with dev_dbg() et al */
 
-struct device_driver xpnet_dbg_name = {
+static struct device_driver xpnet_dbg_name = {
 	.name = "xpnet"
 };
 
-struct device xpnet_dbg_subname = {
+static struct device xpnet_dbg_subname = {
 	.init_name = "",	/* set to "" */
 	.driver = &xpnet_dbg_name
 };
 
-struct device *xpnet = &xpnet_dbg_subname;
+static struct device *xpnet = &xpnet_dbg_subname;
 
 /*
  * Packet was recevied by XPC and forwarded to us.