scsi: ufs: Remove unused min_uA field in struct ufs_vreg

There are two fields related to regulator current limit in struct ufs_vreg:
"min_uA" and "max_uA".

"max_uA" is probed by "<name>-max-microamp" property from device tree and
used for

 - regulator_set_load operations
 - icc_level configuration in device

However "min_uA" field is not used anywhere, thus we can remove it.

Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Reviewed-by: Marc Gonzalez <marc.w.gonzalez@free.fr>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Acked-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>