modules_install: make missing $DEPMOD a warning instead of an error

When $DEPMOD is not found, only print a warning instead of exiting
with an error message and error status.

Warning: 'make modules_install' requires /sbin/depmod. Please install it.
This is probably in the kmod package.

Change-Id: I30663b83a705873b4e2def3b2e8380913d69c450
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Fixes: 934193a ("kbuild: verify that $DEPMOD is installed")
Cc: stable@vger.kernel.org
Cc: Lucas De Marchi <lucas.demarchi@profusion.mobi>
Cc: Lucas De Marchi <lucas.de.marchi@gmail.com>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Chih-Wei Huang <cwhuang@linux.org.tw>
Cc: H. Nikolaus Schaller <hns@goldelico.com>
Reported-by: H. Nikolaus Schaller <hns@goldelico.com>

Author: xiaolusx

scripts/depmod.sh

@@ -16,9 +16,9 @@ if ! test -r System.map ; then
 fi
 
 if [ -z $(command -v $DEPMOD) ]; then
-	echo "'make modules_install' requires $DEPMOD. Please install it." >&2
+	echo "Warning: 'make modules_install' requires $DEPMOD. Please install it." >&2
 	echo "This is probably in the kmod package." >&2
-	exit 1
+	exit 0
 fi
 
 # older versions of depmod don't support -P <symbol-prefix>