Unable to compile the tools in Raspberry Pi

[urbi001]

The current kernel version in my Raspberry Pi is: 4.14.44-v7+.
When I tried to execute:
sudo apt-get install linux-headers-$(uname -r)
==> E: Unable to locate package linux-headers-4.14.44-v7
So, I have updated the firmware using:
$sudo rpi-update
$sudo reboot
Then I search for available linux-headers and linux-image through:
$apt update
$apt-cache search linux-headers
==> raspberrypi-kernel-headers - Header files for the Raspberry Pi Linux Kernel
$ sudo apt-get install raspberrypi-kernel-headers
$apt-cache search linux-image
==> raspberrypi-kernel - Raspberry Pi Bootloader
$ sudo apt-get install raspberrypi-kernel

After this, when I try to execute make defconfig-ath9k-debug,
It is showing: your kernel headers are incomplete/ not installed. Please install kernel headers.
Could you please help me in this regard?