nezha_defconfig: specify 5.19 kernel headers

The defconfig uses a 5.19-rc1 based kernel, so specify 5.19 kernel headers
now that is available.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/nezha_defconfig

@@ -1,6 +1,6 @@
 BR2_riscv=y
 BR2_GLOBAL_PATCH_DIR="board/nezha/patches"
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_17=y
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_19=y
 BR2_SYSTEM_DHCP="eth0"
 BR2_ROOTFS_OVERLAY="board/nezha/overlay"
 BR2_ROOTFS_POST_IMAGE_SCRIPT="support/scripts/genimage.sh"