powerpc: Export dcr_ind_lock to fix build error

Fix build error caused by missing export:

ERROR: "dcr_ind_lock" [drivers/net/ethernet/ibm/emac/ibm_emac.ko] undefined!
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/dcr.c

@@ -230,5 +230,6 @@ EXPORT_SYMBOL_GPL(dcr_unmap_mmio);
 
 #ifdef CONFIG_PPC_DCR_NATIVE
 DEFINE_SPINLOCK(dcr_ind_lock);
+EXPORT_SYMBOL_GPL(dcr_ind_lock);
 #endif	/* defined(CONFIG_PPC_DCR_NATIVE) */