doc: Fix a typo in the description in doc/README.JFFS2_NAND

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
diff --git a/doc/README.JFFS2_NAND b/doc/README.JFFS2_NAND
index 5018ae8..09788d5 100644
--- a/doc/README.JFFS2_NAND
+++ b/doc/README.JFFS2_NAND
@@ -1,6 +1,6 @@
 JFFS2 NAND support:
 
-To ebable, use the following #define in the board configuration file:
+To enable, use the following #define in the board configuration file:
 
 #define CONFIG_JFFS2_NAND 1