btf: Switch vmlinux BTF attribute to sysfs_bin_attr_simple_read()

The generic function from the sysfs core can replace the custom one.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20241228-sysfs-const-bin_attr-simple-v2-2-7c6f3f1767a3@weissschuh.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>