spi: a3700: Remove endianness swapping for full-duplex transfers

spi: a3700: Remove endianness swapping for full-duplex transfers

Fixes the following sparse warnings :
line 767: warning: incorrect type in assignment (different base types)
line 767:    expected unsigned int [unsigned] [assigned] [usertype] val_out
line 767:    got restricted __le32 [usertype] <noident>
line 776: warning: cast to restricted __le32

This takes advantage of readl/writel to do the endianness reordering,
and removes an extra variable in the function.

Fixes: 7bbaa2207e7d ("spi: a3700: Add full-duplex support")
Signed-off-by: Maxime Chevallier <maxime.chevallier@smile.fr>
Reviewed-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>