libbpf-tools: fix dev_t type issue

libbpf-tools: fix dev_t type issue

The vmlinux.h uses u32 to define dev_t. But the user-space process uses
<sys/types.h> which uses 8 bytes for dev_t. When the libbpf uses mapped
memory to update .rodata, it might override other variable's value. We
should use u32 to fix it.

And also fix `biosnoop -d $dev-name` issue.

Signed-off-by: Wei Fu <fuweid89@gmail.com>