storage: Fix path check in storagePoolLookupByTargetPath

storage: Fix path check in storagePoolLookupByTargetPath

Commit id '5ab746b8' introduced the function as perhaps a copy
of storageVolLookupByPath; however, it did not use the @cleanpath
variable even though it used the virFileSanitizePath. So in essance
the only "check" being done for failure is whether it was possible
to strdup the path.

Looking at the virStoragePoolDefParseXML one will note that the
target.path is stored using the result of virFileSanitizePath.
Therefore, this function should sanitize and use the input @path
for the argument to storagePoolLookupByTargetPathCallback which
is comparing against stored target.path values.

Additionally, if there was an error we should use the proper error
of VIR_ERR_NO_STORAGE_POOL (instead of VIR_ERR_NO_STORAGE_VOL).