kernel/locking: Fix compile error with qrwlock.c

Saw these compile errors on SPARC when queued rwlock feature is enabled.

 CC      kernel/locking/qrwlock.o
kernel/locking/qrwlock.c: In function ‘queued_read_lock_slowpath’:
kernel/locking/qrwlock.c:89: error: implicit declaration of function ‘arch_spin_lock’
kernel/locking/qrwlock.c:102: error: implicit declaration of function ‘arch_spin_unlock’
make[4]: *** [kernel/locking/qrwlock.o] Error 1

Include spinlock.h in qrwlock.c to fix it.

Signed-off-by: Babu Moger <babu.moger@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Reviewed-by: Vijay Kumar <vijay.ac.kumar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/locking/qrwlock.c

@@ -20,6 +20,7 @@
 #include <linux/cpumask.h>
 #include <linux/percpu.h>
 #include <linux/hardirq.h>
+#include <linux/spinlock.h>
 #include <asm/qrwlock.h>
 
 /*