alloc_percpu: fix UP build

Impact: build fix

the !SMP branch had a 'gfp' leftover:

 include/linux/percpu.h: In function '__alloc_percpu':
 include/linux/percpu.h:160: error: 'gfp' undeclared (first use in this function)
 include/linux/percpu.h:160: error: (Each undeclared identifier is reported only once
 include/linux/percpu.h:160: error: for each function it appears in.)

Use GFP_KERNEL like the SMP version does.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/percpu.h

@@ -157,7 +157,7 @@ static inline void *__alloc_percpu(size_t size, size_t align)
 	 * percpu sections on SMP for which this path isn't used.
 	 */
 	WARN_ON_ONCE(align > __alignof__(unsigned long long));
-	return kzalloc(size, gfp);
+	return kzalloc(size, GFP_KERNEL);
 }
 
 static inline void free_percpu(void *p)