openpower-pnor: Fix dependency on host-xz

We need host-xz, not host_xz - the latter is invalid. We wouldn't have
seen that previously, as the ifeq check would always been false, given
the string value of OPENPOWER_PNOR_XZ_ENABLED.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/openpower/package/openpower-pnor/openpower-pnor.mk b/openpower/package/openpower-pnor/openpower-pnor.mk
index b314538..cb04f95 100644
--- a/openpower/package/openpower-pnor/openpower-pnor.mk
+++ b/openpower/package/openpower-pnor/openpower-pnor.mk
@@ -25,7 +25,7 @@
 endif
 
 ifeq ($(BR2_OPENPOWER_PNOR_XZ_ENABLED),y)
-OPENPOWER_PNOR_DEPENDENCIES += host_xz
+OPENPOWER_PNOR_DEPENDENCIES += host-xz
 endif