staging: rts5208: rename SG_END macro

A change to the generic scatterlist code caused a conflict with
the rtsx card reader driver:

In file included from drivers/staging/rts5208/rtsx.h:180,
                 from drivers/staging/rts5208/rtsx.c:28:
drivers/staging/rts5208/rtsx_chip.h:343: error: "SG_END" redefined [-Werror]

This changes one instance of the driver to prefix SG_END and
related constants.

Fixes: 723fbf56 ("lib/scatterlist: Add SG_CHAIN and SG_END macros for LSB encodings")
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>