Fix pointer types of winprop_t

Foolish of me to assume the returned window property items have the same
number of bits their format says they have.

Apparently, format = 32 means the return items are 64 bits long (on
64-bit machines).

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/common.h

@@ -235,10 +235,10 @@ typedef struct {
 typedef struct winprop {
   union {
     void *ptr;
-    uint8_t *p8;
-    int16_t *p16;
-    int32_t *p32;
-    uint32_t *c32; // 32bit cardinal
+    char *p8;
+    short *p16;
+    long *p32;
+    unsigned long *c32; // 32bit cardinal
   };
   unsigned long nitems;
   Atom type;