spi: rockchip: Fix PM runtime count on no-op cs

spi: rockchip: Fix PM runtime count on no-op cs

The early bail out that caused an out-of-bounds write was removed with
commit 5c018e378f91 ("spi: spi-rockchip: Fix out of bounds array
access")
Unfortunately that caused the PM runtime count to be unbalanced and
underflowed on the first call. To fix that reintroduce a no-op check
by reading the register directly.

Cc: stable@vger.kernel.org
Fixes: 5c018e378f91 ("spi: spi-rockchip: Fix out of bounds array access")
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/1f2b3af4-2b7a-4ac8-ab95-c80120ebf44c@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>