staging: rtl8723bs: select CONFIG_CRYPTO_LIB_ARC4

The other rtlwifi drivers already have this, but r8723bs
was converted to the generic implementation without adding
the select:

ERROR: modpost: "arc4_crypt" [drivers/staging/rtl8723bs/r8723bs.ko] undefined!
ERROR: modpost: "arc4_setkey" [drivers/staging/rtl8723bs/r8723bs.ko] undefined!

Fixes: 1b11e893 ("staging: rtl8723bs: replace private arc4 encryption with in-kernel one")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210721153550.3624490-1-arnd@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/Kconfig

@@ -5,6 +5,7 @@ config RTL8723BS
 	depends on m
 	select WIRELESS_EXT
 	select WEXT_PRIV
+	select CRYPTO_LIB_ARC4
 	help
 	This option enables support for RTL8723BS SDIO drivers, such as
 	the wifi found on the 1st gen Intel Compute Stick, the CHIP