selftests/livepatch: Replace hardcoded module name with variable in test-callbacks.sh

Replaced the hardcoded module name test_klp_callbacks_demo in the
pre_patch_callback log message with the variable $MOD_LIVEPATCH.

Signed-off-by: George Guo <guodongtai@kylinos.cn>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20241125112812.281018-2-dongtai.guo@linux.dev
Signed-off-by: Petr Mladek <pmladek@suse.com>

Author: georgejguo

tools/testing/selftests/livepatch/test-callbacks.sh

@@ -259,7 +259,7 @@ $MOD_TARGET: ${MOD_TARGET}_init
 % insmod test_modules/$MOD_LIVEPATCH.ko pre_patch_ret=-19
 livepatch: enabling patch '$MOD_LIVEPATCH'
 livepatch: '$MOD_LIVEPATCH': initializing patching transition
-test_klp_callbacks_demo: pre_patch_callback: vmlinux
+$MOD_LIVEPATCH: pre_patch_callback: vmlinux
 livepatch: pre-patch callback failed for object 'vmlinux'
 livepatch: failed to enable patch '$MOD_LIVEPATCH'
 livepatch: '$MOD_LIVEPATCH': canceling patching transition, going to unpatch