Cast the integer read as the first argument for %b to an unsigned integer

so it's value is not sign extended when assigned to the uintmax_t variable
used internally by printf.  For example, if bit 31 is set in the cpuid
feature word, then %b would print out the initial value as a 16 character
hexadecimal value.  Now it only prints out an 8 character value.

Reviewed by:	bde

sys/kern/subr_prf.c

@@ -560,7 +560,7 @@ reswitch:	switch (ch = (u_char)*fmt++) {
 				width = n;
 			goto reswitch;
 		case 'b':
-			num = va_arg(ap, int);
+			num = (u_int)va_arg(ap, int);
 			p = va_arg(ap, char *);
 			for (q = ksprintn(nbuf, num, *p++, NULL); *q;)
 				PCHAR(*q--);