staging : rtl8712: Free memory when kmalloc fails

There are few functions where we need to free previously allocated
memory when kmalloc fails. Else it may lead to memory leakage. In
_init_cmd_priv() and _r8712_init_xmit_priv(), in few places we are
not freeing previously allocated memory when kmalloc fails.

Signed-off-by: Souptick joarder <jrdr.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>