Documentation: sysctl/kernel.txt: fix documentation reference

This patch fixes a reference to Documentation/kmod.txt
which was apparently renamed to Documentation/debugging-modules.txt

Signed-off-by: Michael Opdenacker <[e-mail]>
Cc: "Randy.Dunlap" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/sysctl/kernel.txt

···
 - java-interpreter            [ binfmt_java, obsolete ]
 - kstack_depth_to_print       [ X86 only ]
 - l2cr                        [ PPC only ]
-- modprobe                    ==> Documentation/kmod.txt
+- modprobe                    ==> Documentation/debugging-modules.txt
 - msgmax
 - msgmnb
 - msgmni