ufs: read door bell register after clearing interrupt aggregation

In interrupt context, after reading and comparing the UTRLDBR to
hba->outstanding_request and before resetting the interrupt aggregation,
there might be completion of another transfer request (TR). Such TRs might
get stuck, pending, until the next interrupt is generated (if any).
Changing the sequence of resetting the interrupt aggregation first and
then reading UTRLDBR status, will assure that completed TRs won't get
stuck pending.

Signed-off-by: Dolev Raviv <draviv@codeaurora.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>