[PATCH v1] scsi: ufs-mediatek: Prevent LPM operation on undeclared VCC

[Avri Altman]

> 
> In some platforms, VCC regulator may not be declared in device tree
> to keep itself "always-on". In this case, hba->vreg_info.vcc is NULL
> and shall not be operated during any flow.
> 
> Prevent possible NULL hba->vreg_info.vcc access in LPM mode by checking
> if it is valid first.
> 
> Signed-off-by: Stanley Chu <stanley.chu at mediatek.com>
Reviewed-by: Avri Altman <avri.altman at wdc.com>