Documentation/kbuild: Fix indentation in modules.rst example

Correct the indentation in an example within the `modules.rst` file
to improve readability.

Signed-off-by: Kefan Liu <liukefan24s@ict.ac.cn>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Author: CreeperLKF

Documentation/kbuild/modules.rst

@@ -318,7 +318,7 @@ Several Subdirectories
 		|	|__ include
 		|	    |__ hardwareif.h
 		|__ include
-		|__ complex.h
+			|__ complex.h
 
 	To build the module complex.ko, we then need the following
 	kbuild file::