Fix FAIL: gdb.ada/small_reg_param.exp: continue to call_me

Fix FAIL: gdb.ada/small_reg_param.exp: continue to call_me

If enough information is provided by the compiler, the debugger
now prints the entry value of various parameters:

    (gdb) continue
    Continuing.

    Breakpoint 2, pck.call_me (w=w@entry=50) at [...]
    20            Last_Word := W;

This patch adjusts the expected output to allow an optional
"w@entry=" in the parameter value.

gdb/testsuite/ChangeLog:

        * gdb.ada/small_reg_param.exp: Accept optional entry value
        for parameter "w".