staging: pi433: use DEFINE_SHOW_ATTRIBUTE to simplify pi433_debugfs_regs

Use DEFINE_SHOW_ATTRIBUTE helper macro to simplify the code.
No functional change.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Link: https://lore.kernel.org/r/20220922142548.3248951-1-liushixin2@huawei.com


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