spi: bcm63xx-hsspi: bcmbca-hsspi: fix _be16 type usage

spi: bcm63xx-hsspi: bcmbca-hsspi: fix _be16 type usage

sparse tool report warnings: drivers/spi/spi-bcm63xx-hsspi.c:197:31:
sparse: sparse: cast from restricted __be16.

The controller requires big endian 16 bit data. Define an intermediate
u16 value and use __be16 piointer dereferncing for the data to avoid
directly casting to u16 and sparse warning.

Fixes: 85a84a616999 ("spi: bcm63xx-hsspi: Endianness fix for ARM based SoC")
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202302110438.sQwQnU54-lkp@intel.com/
Signed-off-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20230211032759.72967-1-william.zhang@broadcom.com
Signed-off-by: Mark Brown <broonie@kernel.org>