spi: dw: Avoid stack content exposure

Since "data" is u32, &data is a "u32 *" type, which means pointer math
will move in u32-sized steps. This was meant to be a byte offset, so
cast &data to "char *" to aim the copy into the correct location.

Seen with -Warray-bounds (and found by Coverity):

In file included from ./include/linux/string.h:269,
                 from ./arch/powerpc/include/asm/paca.h:15,
                 from ./arch/powerpc/include/asm/current.h:13,
                 from ./include/linux/mutex.h:14,
                 from ./include/linux/notifier.h:14,
                 from ./include/linux/clk.h:14,
                 from drivers/spi/spi-dw-bt1.c:12:
In function 'memcpy',
    inlined from 'dw_spi_bt1_dirmap_copy_from_map' at drivers/spi/spi-dw-bt1.c:87:3:
./include/linux/fortify-string.h:20:29: warning: '__builtin_memcpy' offset 4 is out of the bounds [0, 4] of object 'data' with type 'u32' {aka 'unsigned int'} [-Warray-bounds]
   20 | #define __underlying_memcpy __builtin_memcpy
      |                             ^
./include/linux/fortify-string.h:191:9: note: in expansion of macro '__underlying_memcpy'
  191 |  return __underlying_memcpy(p, q, size);
      |         ^~~~~~~~~~~~~~~~~~~
drivers/spi/spi-dw-bt1.c: In function 'dw_spi_bt1_dirmap_copy_from_map':
drivers/spi/spi-dw-bt1.c:77:6: note: 'data' declared here
   77 |  u32 data;
      |      ^~~~

Addresses-Coverity: CID 1497771 Out-of-bounds access
Fixes: abf00907 ("spi: dw: Add Baikal-T1 SPI Controller glue driver")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20210211203714.1929862-1-keescook@chromium.org


Signed-off-by: Mark Brown <broonie@kernel.org>