linux: Makefile.postfix: fix typo in postfix target

This adds test results for:
  workflow: blktests
  tree: linux
  ref: v6.15
  test number: 0001
  test result: ok

Detailed test report:

Kernel tests results:

Blktests summary:
Tests run: 1, Passed: 1, Failed: 0

Sample passed test:
runtime	0.442s
trim iops	7000
description	run various discard sizes
exit_status	0
date	2025-09-29 01:53:31
status	pass

Author: kdevops

blktests/gh/linux/20250929/0001/makefile-postfix-fix-typo-in-postfix-target/v6.15.tar.xz

@@ -0,0 +1 @@
+v6.15.xz

blktests/gh/linux/20250929/0001/makefile-postfix-fix-typo-in-postfix-target/v6.15.xz

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:149bfbb5902e658a8ede56ab55635ec9af605ecbbbd05976746159aa185a0213
+size 224980