scsi: ufs: core: Remove redundant desc_size variable from hba

Always read the descriptor with QUERY_DESC_MAX_SIZE.  According to the
spec, the device returns the actual size.

Signed-off-by: Arthur Simchaev <Arthur.Simchaev@wdc.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>