Fix various typos, scattered over the code.

Spelling corrections for (among other things):

* environment
* override
* variable
* ftd (should be "fdt", for flattened device tree)
* embedded
* FTDI
* emulation
* controller
diff --git a/drivers/dfu/Kconfig b/drivers/dfu/Kconfig
index 4fe2219..6b92064 100644
--- a/drivers/dfu/Kconfig
+++ b/drivers/dfu/Kconfig
@@ -3,8 +3,8 @@
 config DFU_TFTP
 	bool "DFU via TFTP"
 	help
-	  This option allows performing update of DFU managed medium with data
-	  send via TFTP boot.
-	  Detailed description of this feature can be found at ./doc/README.dfutftp
+	  This option allows performing update of DFU-managed medium with data
+	  sent via TFTP boot.
 
+	  Detailed description of this feature can be found at ./doc/README.dfutftp
 endmenu