staging: rtl8192e: Make use kmemdup

As kmemdup API does kmalloc + memcpy . We can make use of it instead of
calling kmalloc and memcpy independetly.

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Link: https://lore.kernel.org/r/20190804024832.GA14352@hari-Inspiron-1545


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