Ignore -Wformat warning

Clang 6.0.1 update introduced a number of new warnings, failing
werror build. Ignore the -Wformat warning for external/libese.

Test: m checkbuild
Change-Id: Ie82a0cc86a49682c9189d0af8b86008d88a32f54
diff --git a/libese-hw/nxp/Android.bp b/libese-hw/nxp/Android.bp
index 506a32a..0ec4ea6 100644
--- a/libese-hw/nxp/Android.bp
+++ b/libese-hw/nxp/Android.bp
@@ -31,6 +31,7 @@
         "-Wall",
         "-Werror",
         "-Wno-error=unused-variable",
+        "-Wno-format",
     ],
     target: {
         darwin: {
@@ -61,6 +62,9 @@
     name: "libese-hw-nxp-pn80t-spidev",
     defaults: ["pn80t_platform"],
     srcs: ["pn80t/linux_spidev.c"],
+    cflags: [
+        "-Wno-format",
+    ],
 }
 
 cc_library {
@@ -71,5 +75,6 @@
         "-Wall",
         "-Werror",
         "-Wno-error=unused-variable",
+        "-Wno-format",
     ],
 }