kbuild: rpm-pkg: pass 'linux' to --target option of rpmbuild

Presumably, _target_os is defined even if the --target flag does not
specify it, but it is better to make it explicit.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.package

@@ -56,7 +56,7 @@ rpm-pkg:
 	$(MAKE) clean
 	$(CONFIG_SHELL) $(MKSPEC) >$(objtree)/kernel.spec
 	$(call cmd,src_tar,$(KERNELPATH),kernel.spec)
-	+rpmbuild $(RPMOPTS) --target $(UTS_MACHINE) -ta $(KERNELPATH).tar.gz \
+	+rpmbuild $(RPMOPTS) --target $(UTS_MACHINE)-linux -ta $(KERNELPATH).tar.gz \
 	--define='_smp_mflags %{nil}'
 
 # binrpm-pkg
@@ -66,7 +66,7 @@ binrpm-pkg:
 	$(MAKE) -f $(srctree)/Makefile
 	$(CONFIG_SHELL) $(MKSPEC) prebuilt > $(objtree)/binkernel.spec
 	+rpmbuild $(RPMOPTS) --define "_builddir $(objtree)" --target \
-		$(UTS_MACHINE) -bb $(objtree)/binkernel.spec
+		$(UTS_MACHINE)-linux -bb $(objtree)/binkernel.spec
 
 PHONY += deb-pkg
 deb-pkg: