* amd64-tdep.c (amd64_return_value): Change type of readbuf and

* amd64-tdep.c (amd64_return_value): Change type of readbuf and
writebuf arguments to `gdb_byte *'.  Remove now redundant casts.
* i386-tdep.c (i386_return_value): Change type of readbuf and
writebuf arguments to `gdb_byte *'.
(i386_pseudo_register_read, i386_pseudo_register_write): Change
type of last argument to `gdb_byte *'.
(i386_register_to_value, i386_value_to_register): Change type of
last argument to `gdb_byte *'.  Simplify function a bit.
* i387-tdep.h (i387_value_to_register, i387_register_to_value):
Change type of last argument to `gdb_byte *'.
* i387-tdep.c: Likewise.