nvme-cli: Fix build on aarch64-linux-android-4.9

nvme-cli: Fix build on aarch64-linux-android-4.9

Need to include sys/stat.h to fix:
fabrics.c:414:45: error: 'S_IRUSR' undeclared (first use in this function)
fabrics.c:414:53: error: 'S_IWUSR' undeclared (first use in this function)

Also fix warning:
common.h:4:0:
warning: "offsetof" redefined #define offsetof(x, y)
__builtin_offsetof(x, y) ^

Fix this trivial warning by including stddef.h and removing this
definition.

Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <keith.busch@intel.com>