scripts: checkpatch: fix word splitting in the command

The following would fail with Zsh instead of Bash :
$ source ./scripts/checkpatch_inc.sh
$ checkpatch HEAD
Unknown option: typedefsfile typedefs.checkpatch
Usage: .../scripts/checkpatch.pl [OPTION]... [FILE]

By setting xtrace in the _checkpatch() function, we can see the built
command is interpreted differently depending on the shell:
	$CHECKPATCH $CHECKPATCH_OPT $typedefs_opt -
In Zsh:
	/scripts/checkpatch.pl '--typedefsfile typedefs.checkpatch' -
In Bash:
	/scripts/checkpatch.pl --typedefsfile typedefs.checkpatch -

Bash differs from Zsh when it comes to word splitting for unquoted
parameters expansions.
One solution is to use `eval` to execute the built command.

Signed-off-by: Clement Faure <clement.faure@nxp.com>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>

scripts/checkpatch_inc.sh

@@ -23,7 +23,7 @@ function _checkpatch() {
 				typedefs_opt="";
 		# Ignore NOT_UNIFIED_DIFF in case patch has no diff
 		# (e.g., all paths filtered out)
-		$CHECKPATCH $CHECKPATCH_OPT $typedefs_opt -
+		eval "$CHECKPATCH $CHECKPATCH_OPT $typedefs_opt -"
 }
 
 function checkpatch() {