crimson: use uint32_t when calling ioctl(BLKGETNRZONES)

crimson: use uint32_t when calling ioctl(BLKGETNRZONES)

before this change, we pass a pointer to a `size_t` to
ioctl(BLKGETNRZONES), but in the Linux kernel,
include/uapi/linux/blkzoned.h:

```c
 #define BLKGETNRZONES	_IOR(0x12, 133, __u32)
```
this API reads 32 bits of data into the pointer. on 64-bit
architectures, size_t is 64 bits. fortunately, we initialize
nr_zones with 0, so the upper 32 bits remain zero. this works
on little-endian systems, but not on big-endian systems. it is
also semantically wrong. we should pass a pointer to a 32-bit
value when calling ioctl(BLKGETNRZONES).

in this change, we change the type of nr_zones from size_t to
uint32_t to match what the Linux kernel expects.

Signed-off-by: Kefu Chai <k.chai@proxmox.com>