[IA64] Remove sparse warning from unwind code

Running ia64 through sparse gives warnings in the unwind code.

include/asm-ia64/unwind.h:84:17: error: dubious bitfield without explicit `signed' or `unsigned'

Make the bitfield explicitly unsigned.

Signed-off-by: Keith Owens <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>

include/asm-ia64/unwind.h

···
 	struct unw_ireg {
 		unsigned long *loc;
 		struct unw_ireg_nat {
-			long type : 3;			/* enum unw_nat_type */
+			unsigned long type : 3;		/* enum unw_nat_type */
 			signed long off : 61;		/* NaT word is at loc+nat.off */
 		} nat;
 	} r4, r5, r6, r7;