ada-lang.c:ada_find_renaming_symbol minor improvement.

ada-lang.c:ada_find_renaming_symbol minor improvement.

This is a minor improvement in ada_find_renaming_symbol: What we were
doing was going from a symbol, get its name, and then search for
renamings.  But if the original symbol was already itself a renaming,
then we'd look the symbol up again to return it.  Since we had the
symbol in the first place, we shouldn't need to look it up again.

This is what this patch does: Modify ada_find_renaming_symbol to
take a symbol instead of the symbol's (linkage) name, and then updates
the one caller.

gdb/ChangeLog:

        * ada-lang.h (ada_find_renaming_symbol): Replace parameter
        "name" with "struct symbol *name_sym".
        * ada-exp.y (write_var_or_type): Update call to
        ada_find_renaming_symbol.
        * ada-lang.c (ada_find_renaming_symbol): Replace parameter
        "name" with "struct symbol *name_sym". Adjust Implementation
        accordingly.  Adjust the function documentation.