cifs: Fix some error pointers handling detected by static checker

* extract_hostname() and extract_sharename() never return NULL, so
  use IS_ERR() instead of IS_ERR_OR_NULL() in cifs_find_swn_reg(). If
  any of these functions return an error, then return an error pointer
  instead of NULL.
* Change cifs_find_swn_reg() function to always return a valid pointer
  or an error pointer, instead of returning NULL if the registration
  is not found.
* Finally update cifs_find_swn_reg() callers to check for -EEXIST
  instead of NULL.
* In cifs_get_swn_reg() the swnreg idr mutex was not unlocked in the
  error path of cifs_find_swn_reg() call.

Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Samuel Cabrero <[email protected]>
Reviewed-by: Dan Carpenter <[email protected]>
Signed-off-by: Steve French <[email protected]>

0 files changed, 0 insertions, 0 deletions