staging: rtl8712: rtl871x_mp_ioctl: Move a large data struct onto the heap

staging: rtl8712: rtl871x_mp_ioctl: Move a large data struct onto the heap

Fixes the following W=1 kernel build warning(s):

 drivers/staging/rtl8712/rtl871x_mp_ioctl.c: In function ‘mp_start_test’:
 drivers/staging/rtl8712/rtl871x_mp_ioctl.c:204:1: warning: the frame size of 1136 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Florian Schilhabel <florian.c.schilhabel@googlemail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Zhansaya Bagdauletkyzy <zhansayabagdaulet@gmail.com>
Cc: Michael Straube <straube.linux@gmail.com>
Cc: WLAN FAE <wlanfae@realtek.com>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210414181129.1628598-21-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>