lib/alloc_tag: use %pe format specifier

lib/alloc_tag: use %pe format specifier

The %pe format specifier is designed to print error pointers.  It prints a
symbolic error name (eg.  -EINVAL) and it makes the code simpler by
omitting PTR_ERR();

This patch fixes this cocci report:
lib/alloc_tag.c:776:63-70: WARNING: Consider using %pe to print PTR_ERR()

Link: https://lkml.kernel.org/r/20251105023925.1447482-1-zeng_chi911@163.com
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Acked-by: SeongJae Park <sj@kernel.org>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>