gn.bbclass: Remove erroneous -C gn command switch

gn docs state that the output dir should be passed as a last argument of the
gn gen command without any preceding switch

Signed-off-by: Robert Drab <robert.drab@huawei.com>

meta-ohos-staging/classes/gn.bbclass

@@ -39,7 +39,7 @@ B = "${WORKDIR}/out"
 
 gn_do_configure() {
     cd ${S}
-    gn gen ${GN_OPTIONS} --args='${GN_ARGS}' -C ${B}
+    gn gen ${GN_OPTIONS} --args='${GN_ARGS}' ${B}
 }
 
 gn_do_compile() {