checkpatch: Change occurences of 'kernel' to 'qemu' in user messages

It is odd that we inform user that, for example, his current working
directory is not kernel root, when, in face, we mean qemu root.

Replace that and few other similar odd user messages.

Signed-off-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Message-Id: <20200620133207.26849-3-aleksandar.qemu.devel@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

scripts/checkpatch.pl

@@ -49,7 +49,7 @@ Version: $V
 
 Options:
   -q, --quiet                quiet
-  --no-tree                  run without a kernel tree
+  --no-tree                  run without a qemu tree
   --no-signoff               do not check for 'Signed-off-by' line
   --patch                    treat FILE as patchfile
   --branch                   treat args as GIT revision list
@@ -57,7 +57,7 @@ Options:
   --terse                    one line per report
   -f, --file                 treat FILE as regular source file
   --strict                   fail if only warnings are found
-  --root=PATH                PATH to the kernel tree root
+  --root=PATH                PATH to the qemu tree root
   --no-summary               suppress the per-file summary
   --mailback                 only produce a report in case of warnings/errors
   --summary-file             include the filename in summary
@@ -203,7 +203,7 @@ if ($tree) {
 	}
 
 	if (!defined $root) {
-		print "Must be run from the top-level dir. of a kernel tree\n";
+		print "Must be run from the top-level dir. of a qemu tree\n";
 		exit(2);
 	}
 }