scsi: ufs: wb: Change wb_enabled condition test

Change to improve readability.

Link: https://lore.kernel.org/r/20220804074928epcms2p86582693a39597501b491400a28543a92@epcms2p8


Reviewed-by: Avri Altman <avri.altman@wdc.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Jinyoung Choi <j-young.choi@samsung.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>