asm-generic/io.h: suppress endianness warnings for readq() and writeq()

Commit c1d55d50

 ("asm-generic/io.h: Fix sparse warnings on
big-endian architectures") missed fixing the 64-bit accessors.

Arnd explains in the attached link why the casts are necessary, even if
__raw_readq() and __raw_writeq() do not take endian-specific types.

Link: https://lore.kernel.org/lkml/9105d6fc-880b-4734-857d-e3d30b87ccf6@app.fastmail.com/
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>