meta-phosphor: gpioplus: cleanup oeconf options

Cleanup the extra oeconf variable in the recipe such that it's an
assignment and not an append and isn't a mixed-evaluation line.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ic74a914ce3621c6a8e3415d61218a0acf1e99ad0
diff --git a/recipes-extended/gpioplus/gpioplus_git.bb b/recipes-extended/gpioplus/gpioplus_git.bb
index e2c960b..d60310e 100644
--- a/recipes-extended/gpioplus/gpioplus_git.bb
+++ b/recipes-extended/gpioplus/gpioplus_git.bb
@@ -12,10 +12,7 @@
         autoconf-archive-native \
         "
 
-EXTRA_OECONF_append += " \
-        --disable-examples \
-        --disable-tests \
-        "
+EXTRA_OECONF = "--disable-examples --disable-tests"
 
 SRC_URI += "git://github.com/openbmc/gpioplus"
 SRCREV = "48e6288da8486a25fd52e944fb0f7148fc1c02db"