Add missing error code from libzfs

EZFS_ASHIFT_MISMATCH added to libzfs.h, but since it was not present
in py-libzfs, the error codes were out of sync. This commit fixes
this.

Signed-off-by: Umer Saleem <usaleem@ixsystems.com>
(cherry picked from commit b898879)

pxd/libzfs.pxd

@@ -178,6 +178,7 @@ cdef extern from "libzfs.h" nogil:
         EZFS_RESUME_EXISTS
         EZFS_SHAREFAILED
         EZFS_RAIDZ_EXPAND_IN_PROGRESS
+        EZFS_ASHIFT_MISMATCH
         EZFS_UNKNOWN
 
     IF HAVE_ZFS_ENCRYPTION: