Minor tweak of usage of sha256 in bsd.port.mk

bsd.port.mk factors out the current cipher (sha256) for hashes to _CIPHER.
However, in two places, it uses sha256 directly. This patch just changes
those spots to use ${_CIPHER} like the rest of the file.

OK?

--Kurt

Index: bsd.port.mk
===================================================================
RCS file: /cvs/ports/infrastructure/mk/bsd.port.mk,v
retrieving revision 1.1477
diff -u -p -r1.1477 bsd.port.mk
--- bsd.port.mk 26 Aug 2019 23:38:12 -0000 1.1477
+++ bsd.port.mk 15 Sep 2019 23:19:55 -0000
@@ -1680,8 +1680,8 @@ _PACKAGE_CHECKSUM_DIR = ${PACKAGE_REPOSI
_do_checksum_package = \
install -d ${PACKAGE_REPOSITORY_MODE} ${_PACKAGE_CHECKSUM_DIR} && \
cd ${_TMP_REPO} && \
- cksum -b -a sha256 -- $$pkgname \
- >${_PACKAGE_CHECKSUM_DIR}/$$(basename $$pkgname .tgz).sha256
+ cksum -b -a ${_CIPHER} -- $$pkgname \
+ >${_PACKAGE_CHECKSUM_DIR}/$$(basename $$pkgname .tgz).${_CIPHER}

.if ${CHECKSUM_PACKAGES:L} == "yes"
_checksum_package = ${_do_checksum_package}