package/pkg-generic.mk: Set <pkg>_CPE_ID_UPDATE to NA by default

The commit [1] set the default value of '<pkg>_CPE_ID_UPDATE' to not use
a wildcard by default. But instead of setting the value to '-' it set it
to an empty value instead.

According to document [2] section 6.1.2.1.1 the 'Not Attributed' value
bind to an hyphen ('-') and the blank statement bind to the 'Any' ('*').

Because the CPE matching function was incorrect using a blank statement
worked to remove the false positives but this is not correct according
to the CPE documentation.

[1] 53a8616460 package/pkg-generic.mk: use more sensible default value for <pkg>_CPE_ID_UPDATE
[2] https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nistir7695.pdf

Fixes: 53a8616460e5730abe703ca5a46bae0039d548aa.
Signed-off-by: Thomas Perale <thomas.perale@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/pkg-generic.mk

@@ -727,6 +727,8 @@ ifeq ($$($(2)_CPE_ID_VALID),YES)
  ifndef $(2)_CPE_ID_UPDATE
   ifdef $(3)_CPE_ID_UPDATE
    $(2)_CPE_ID_UPDATE = $$($(3)_CPE_ID_UPDATE)
+  else
+   $(2)_CPE_ID_UPDATE = -
   endif
  endif