Kconfig: fix spelling

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/Kconfig b/Kconfig
index aff7b2e..a078f7b 100644
--- a/Kconfig
+++ b/Kconfig
@@ -213,7 +213,7 @@
 	help
 	  Say Y here to support 64bit physical memory address.
 	  This can be used not only for 64bit SoCs, but also for
-	  large physical address extention on 32bit SoCs.
+	  large physical address extension on 32bit SoCs.
 
 config BUILD_ROM
 	bool "Build U-Boot as BIOS replacement"