iio: frequency: adrf6780: Fix adrf6780_spi_{read,write}()

iio: frequency: adrf6780: Fix adrf6780_spi_{read,write}()

Clang warns:

drivers/iio/frequency/adrf6780.c:117:1: error: all paths through this
function will call itself [-Werror,-Winfinite-recursion]
{
^
drivers/iio/frequency/adrf6780.c:138:1: error: all paths through this
function will call itself [-Werror,-Winfinite-recursion]
{
^
2 errors generated.

The underscore variants should be used here.

Link: https://github.com/ClangBuiltLinux/linux/issues/1490
Fixes: 63aaf6d06d87 ("iio: frequency: adrf6780: add support for ADRF6780")
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20211022195656.1513147-1-nathan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>