staging: rtl8723bs: fix unmet dependency on CRYPTO for CRYPTO_LIB_ARC4

When RTL8723BS is selected, and CRYPTO is not selected,
Kbuild gives the following warning:

WARNING: unmet direct dependencies detected for CRYPTO_LIB_ARC4
Depends on [n]: CRYPTO [=n]
Selected by [m]:
- RTL8723BS [=m] && STAGING [=y] && WLAN [=y] && MMC [=y] && CFG80211 [=y] && m && MODULES [=y]
- RTLLIB_CRYPTO_WEP [=m] && STAGING [=y] && RTLLIB [=m]

This is because RTL8723BS selects CRYPTO_LIB_ARC4
without selecting CRYPTO, despite CRYPTO_LIB_ARC4
depending on CRYPTO.

This unmet dependency bug was detected by Kismet,
a static analysis tool for Kconfig. Please advise
if this is not the appropriate solution.

Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Julian Braha <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/rtl8723bs/Kconfig

···
 	depends on WLAN && MMC && CFG80211
 	depends on m
 	select CFG80211_WEXT
+	select CRYPTO
 	select CRYPTO_LIB_ARC4
 	help
 	This option enables support for RTL8723BS SDIO drivers, such as