Code:
SQL> select * from xyz;

        ID NAME                        SAL
---------- -------------------- ----------
         1 joe
         2 sally
         3 pete
         4 pete                       2222
         5 joe                        3333
         6 sally                      7777
         7 kelly                      4444

7 rows selected.

SQL> update xyz x
        set sal = (
           select max(sal) 
           from xyz y 
           where sal is not null and y.name = x.name)
/

7 rows updated.

SQL> select * from xyz;

        ID NAME                        SAL
---------- -------------------- ----------
         1 joe                        3333
         2 sally                      7777
         3 pete                       2222
         4 pete                       2222
         5 joe                        3333
         6 sally                      7777
         7 kelly                      4444

7 rows selected.