staging: rtl8712: consolidate kmalloc + memset 0 to kzalloc

This is an API consolidation only. The use of kmalloc + memset to 0
here is equivalent to kzalloc.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>