[IA64] fix build warning in arch/ia64/oprofile/backtrace.c

arch/ia64/oprofile/backtrace.c:63: warning: comparison of distinct pointer types lacks a cast

Comparing a "u64 *" with an "unsigned long *". Make them match.
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/oprofile/backtrace.c

@@ -29,7 +29,7 @@ typedef struct
 	unsigned int depth;
 	struct pt_regs *regs;
 	struct unw_frame_info frame;
-	u64 *prev_pfs_loc;	/* state for WAR for old spinlock ool code */
+	unsigned long *prev_pfs_loc;	/* state for WAR for old spinlock ool code */
 } ia64_backtrace_t;
 
 /* Returns non-zero if the PC is in the Interrupt Vector Table */