io_uring: make io_uring_sqe_cmd() unconditionally available

If CONFIG_IO_URING isn't set, then io_uring_sqe_cmd() is not defined.
As the nvme driver uses this helper, it causes a compilation issue:

 drivers/nvme/host/ioctl.c: In function 'nvme_uring_cmd_io':
 drivers/nvme/host/ioctl.c:555:44: error: implicit declaration of function 'io_uring_sqe_cmd'; did you mean 'io_uring_free'? [-Werror=implicit-function-declaration]
   555 |         const struct nvme_uring_cmd *cmd = io_uring_sqe_cmd(ioucmd->sqe);
       |                                            ^~~~~~~~~~~~~~~~
       |                                            io_uring_free

Fix it by just making io_uring_sqe_cmd() generally available - the types
are known, and there's no reason to hide it under CONFIG_IO_URING.

Fixes: fd9b854 ("io_uring: Pass whole sqe to commands")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Chen-Yu Tsai <wenst@chromium.org>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

include/linux/io_uring.h

@@ -36,6 +36,11 @@ struct io_uring_cmd {
 	u8		pdu[32]; /* available inline for free use */
 };
 
+static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe)
+{
+	return sqe->cmd;
+}
+
 #if defined(CONFIG_IO_URING)
 int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
 			      struct iov_iter *iter, void *ioucmd);
@@ -66,11 +71,6 @@ static inline void io_uring_free(struct task_struct *tsk)
 	if (tsk->io_uring)
 		__io_uring_free(tsk);
 }
-
-static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe)
-{
-	return sqe->cmd;
-}
 #else
 static inline int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw,
 			      struct iov_iter *iter, void *ioucmd)