Fix compile breakage with kref.h

This set of build failures just started appearing on parisc:

In file included from drivers/input/serio/serio_raw.c:12:
include/linux/kref.h: In function 'kref_get':
include/linux/kref.h:40: error: 'TAINT_WARN' undeclared (first use in this function)
include/linux/kref.h:40: error: (Each undeclared identifier is reported only once
include/linux/kref.h:40: error: for each function it appears in.)
include/linux/kref.h: In function 'kref_sub':
include/linux/kref.h:65: error: 'TAINT_WARN' undeclared (first use in this function)

It happens because TAINT_WARN is defined in kernel.h and this particular
compile doesn't seem to include it (no idea why it's just manifesting ..
probably some #include file untangling exposed it).

Fix by adding

#include <linux/kernel.h>

to linux/kref.h

Signed-off-by: James Bottomley <[e-mail]>
Acked-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/kref.h

···
 
 #include <linux/bug.h>
 #include <linux/atomic.h>
+#include <linux/kernel.h>
 
 struct kref {
 	atomic_t refcount;