cfi_flash: Fix spelling of "Unknown"

"Unkown" should be spelled "Unknown".

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Signed-off-by: Stefan Roese <sr@denx.de>

drivers/mtd/cfi_flash.c

@@ -1140,7 +1140,7 @@ int flash_erase(flash_info_t *info, int s_first, int s_last)
 				break;
 #endif
 			default:
-				debug("Unkown flash vendor %d\n",
+				debug("Unknown flash vendor %d\n",
 				       info->vendor);
 				break;
 			}