spi: npcm: fix u32 csgpio being checked for less than zero

The u32 variable csgpio is being checked for an error return
from the call to of_get_named_gpio, however, since this is unsigned
this comparison will always be false. Fix this by making csgpio an
int and fix up the %u format specifiers to %d accordingly.

Detected by CoverityScan, CID#1475476 ("Unsigned compared against 0")

Fixes: 2a22f1b3 ("spi: npcm: add NPCM PSPI controller driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>