net: ks8851: fix link error

An object file cannot be built for both loadable module and built-in
use at the same time:

arm-linux-gnueabi-ld: drivers/net/ethernet/micrel/ks8851_common.o: in function `ks8851_probe_common':
ks8851_common.c:(.text+0xf80): undefined reference to `__this_module'

Change the ks8851_common code to be a standalone module instead,
and use Makefile logic to ensure this is built-in if at least one
of its two users is.

Fixes: 797047f875b5 ("net: ks8851: Implement Parallel bus operations")
Link: https://lore.kernel.org/netdev/[e-mail]/
Reviewed-by: Andrew Lunn <[e-mail]>
Acked-by: Marek Vasut <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/micrel/Makefile

···
 #
 
 obj-$(CONFIG_KS8842) += ks8842.o
-obj-$(CONFIG_KS8851) += ks8851.o
-ks8851-objs = ks8851_common.o ks8851_spi.o
-obj-$(CONFIG_KS8851_MLL) += ks8851_mll.o
-ks8851_mll-objs = ks8851_common.o ks8851_par.o
+obj-$(CONFIG_KS8851) += ks8851_common.o ks8851_spi.o
+obj-$(CONFIG_KS8851_MLL) += ks8851_common.o ks8851_par.o
 obj-$(CONFIG_KSZ884X_PCI) += ksz884x.o

drivers/net/ethernet/micrel/ks8851_common.c

···
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(ks8851_suspend);
 
 int ks8851_resume(struct device *dev)
 {
···
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(ks8851_resume);
 #endif
 
 static int ks8851_register_mdiobus(struct ks8851_net *ks, struct device *dev)
···
 err_reg_io:
 	return ret;
 }
+EXPORT_SYMBOL_GPL(ks8851_probe_common);
 
 int ks8851_remove_common(struct device *dev)
 {
···
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(ks8851_remove_common);
+
+MODULE_DESCRIPTION("KS8851 Network driver");
+MODULE_AUTHOR("Ben Dooks <[e-mail]>");
+MODULE_LICENSE("GPL");