misc: eeprom/idt_89hpesx: Switch to memdup_user_nul() helper

Use memdup_user_nul() helper instead of open-coding to simplify the code.

Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://lore.kernel.org/r/20230810121608.2110328-1-ruanjinjie@huawei.com


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