LU-5221 vvp: release mmap_sem in error case

The mmap_sem is downed in vvp_mmap_locks, but in case of
error from cl_io_lock_alloc_add, it is not upped.

Credit to Paul Casella at Cray for finding this.

Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: If172e7cb4c4e6400143d76eee8aa595ae767a20c
Reviewed-on: http://review.whamcloud.com/10741
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>