kbuild: don't hardcode depmod path

kbuild: don't hardcode depmod path

BugLink: https://bugs.launchpad.net/bugs/1913486
commit 436e980e2ed526832de822cbf13c317a458b78e1 upstream.

depmod is not guaranteed to be in /sbin, just let make look for
it in the path like all the other invoked programs

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: William Breathitt Gray <william.gray@canonical.com>