Fix misc spelling errors found by lintian

Signed-off-by: Loïc Minier <loic.minier@linaro.org>
diff --git a/drivers/net/at91_emac.c b/drivers/net/at91_emac.c
index 4e5685c..90eb515 100644
--- a/drivers/net/at91_emac.c
+++ b/drivers/net/at91_emac.c
@@ -93,7 +93,7 @@
 #define RBF_MULTICAST (1<<30)
 #define RBF_UNICAST   (1<<29)
 #define RBF_EXTERNAL  (1<<28)
-#define RBF_UNKOWN    (1<<27)
+#define RBF_UNKNOWN   (1<<27)
 #define RBF_SIZE      0x07ff
 #define RBF_LOCAL4    (1<<26)
 #define RBF_LOCAL3    (1<<25)