staging: rtl8188: avoid excessive stack usage

The rtl8188 copy of the os_dep support code causes a
warning about a very significant stack usage in the translate_scan()
function:

drivers/staging/rtl8188eu/os_dep/ioctl_linux.c: In function 'translate_scan':
drivers/staging/rtl8188eu/os_dep/ioctl_linux.c:306:1: error: the frame size of 1560 bytes is larger than 1400 bytes [-Werror=frame-larger-than=]

Use the same trick as in the rtl8723bs copy of the same function, and
allocate it dynamically.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200104214832.558198-1-arnd@arndb.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>