staging: r8188eu: Use kmemdup() to replace kmalloc + memcpy

fix memdup.cocci warning:
drivers/staging/r8188eu/os_dep/ioctl_linux.c:4452:33-40: WARNING opportunity for kmemdup

Generated by: scripts/coccinelle/api/memdup.cocci

Signed-off-by: Kai Song <songkai01@inspur.com>
Link: https://lore.kernel.org/r/20211003072841.215903-1-songkai01@inspur.com


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