perl: avoid using += with an over-ride

Using += with an over-ride can be a source of confusion so try to
avoid the construct in core recipes.

(From OE-Core rev: 2588c2aae11b7b480022dc11575295fdc792bf3f)

Signed-off-by: Andre McCurdy <armccurdy@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/perl/perl-native_5.24.4.bb

@@ -135,5 +135,5 @@ EOF
 
 # Fix the path in sstate
 SSTATE_SCAN_FILES += "*.pm *.pod *.h *.pl *.sh"
-PACKAGES_DYNAMIC_class-native += "^perl-module-.*native$"
 
+PACKAGES_DYNAMIC_class-native = "^perl-module-.*native$"

meta/recipes-devtools/perl/perl_5.24.4.bb

@@ -339,7 +339,7 @@ python split_perl_packages () {
 }
 
 PACKAGES_DYNAMIC += "^perl-module-.*(?<!\-native)$"
-PACKAGES_DYNAMIC_class-nativesdk += "^nativesdk-perl-module-.*"
+PACKAGES_DYNAMIC_class-nativesdk = "^nativesdk-perl-module-.*"
 
 RPROVIDES_perl-lib = "perl-lib"