Fix the following compilation warning:

drivers/scsi/ufs/ufshcd.c:2076:5: warning: no previous prototype for
 ufshcd_query_descriptor_retry  [-Wmissing-prototypes]

Also do not export the function, it should not be used out of ufs
context.
Signed-off-by: NTomas Winkler <tomas.winkler@intel.com>
Reviewed-by: NSubhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>