fix bug of fail to prepareCall("{CALL func()}")

Now,the result of JDBC escape syntax for call statements is as following
prepareCall("{call func()}")  OK
prepareCall("{cALL func()}")  OK
prepareCall("{CALL func()}") NG
prepareCall("?={CALL func()}") OK

Consider other cases,the keyword 'call' is case insensitive,and the result of prepareCall("{CALL func()}")  should be OK.