staging: rtl8723bs: use guard clause for stainfo check

staging: rtl8723bs: use guard clause for stainfo check

Continue the refactor of rtw_aes_decrypt() by introducing a guard
clause for the stainfo check. This allows the subsequent multicast
and unicast decryption logic to be moved one indentation level to
the left, further improving code readability.

Signed-off-by: Lin YuChen <starpt.official@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/20260319120737.29692-3-starpt.official@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>