scsi: ufs: Release rw_sem while sending device management requests

Consider the below scenario:
1. Clock scaling is running
   - releases rw_sem before sending hibern8
    - issues hibern8 enter
      - error in hibern8 [1]
      - triggers error-handler(eh) [3]
   - waits on acquiring rw_sem [5]
2. Exception is raised by device
   - acquires rw_sem (if eh not running)as part of
     sending device management reqs [2]
   - returns whithout releasing rw_sem
   (as eh starts running in between) [4]

Here, [5] waits on [2] which acquires rw_sem but does not release,
as eh[3] starts running in between [2] and [4]. Fix this by releasing
rw_sem in ufshcd_exec_dev_cmd() if it was indeed acquired.

Change-Id: Ic6bb9f25e25bff6b8798bb39ea150e920e5bc1a2
Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>