[libpng] Fix build for qemu

* Fix BUILD file when compiling for qemu

Fixed: 87754
Change-Id: I441e04cc5b3b5a72802adcb97af5ce9e8edb2f8a
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/libpng/+/615522
Reviewed-by: David Reveman <reveman@google.com>

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index ea5683a..2f0ec68 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -58,8 +58,8 @@
   cflags = []
   if (current_cpu == "x86" || current_cpu == "x64") {
     sources += [
-      "contrib/intel/filter_sse2_intrinsics.c",
-      "contrib/intel/intel_init.c",
+      "intel/filter_sse2_intrinsics.c",
+      "intel/intel_init.c",
     ]
     defines += [ "PNG_INTEL_SSE_OPT=1" ]
   } else if ((current_cpu == "arm" || current_cpu == "arm64") && arm_use_neon) {