Update to v5.15 kernel headers.

Kernel headers coming from:

Git: https://android.googlesource.com/kernel/common/
Branch: android-mainline
Tag: android-mainline-5.15

Test: Builds, and ran bionic unit tests on flame.
Change-Id: I86901ea6d89fb0f7384b90a47bef35d194083c24
diff --git a/libc/kernel/uapi/linux/version.h b/libc/kernel/uapi/linux/version.h
index a2528a6..71a3f77 100644
--- a/libc/kernel/uapi/linux/version.h
+++ b/libc/kernel/uapi/linux/version.h
@@ -16,8 +16,8 @@
  ***
  ****************************************************************************
  ****************************************************************************/
-#define LINUX_VERSION_CODE 331264
+#define LINUX_VERSION_CODE 331520
 #define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + ((c) > 255 ? 255 : (c)))
 #define LINUX_VERSION_MAJOR 5
-#define LINUX_VERSION_PATCHLEVEL 14
+#define LINUX_VERSION_PATCHLEVEL 15
 #define LINUX_VERSION_SUBLEVEL 0