spi/atmel: typo in debug message

This patches a typo in the debug message.

Signed-off-by: Matthias Brugger <mensch0815@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
index 5c03a5b..154529a 100644
--- a/drivers/spi/atmel_spi.c
+++ b/drivers/spi/atmel_spi.c
@@ -679,7 +679,7 @@
 			bits = (asd->csr >> 4) & 0xf;
 			if (bits != xfer->bits_per_word - 8) {
 				dev_dbg(&spi->dev, "you can't yet change "
-					 "bit_per_word in transfers\n");
+					 "bits_per_word in transfers\n");
 				return -ENOPROTOOPT;
 			}
 		}