init: move cifs_root_data() prototype into linux/mount.h

cifs_root_data() is defined in cifs and called from early init code, but
lacks a global prototype:

fs/cifs/cifsroot.c:83:12: error: no previous prototype for 'cifs_root_data'

Move the declaration from do_mounts.c into an appropriate header.

Link: https://lkml.kernel.org/r/20230517131102.934196-13-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Eric Paris <eparis@redhat.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mount.h

@@ -124,4 +124,6 @@ extern int iterate_mounts(int (*)(struct vfsmount *, void *), void *,
 			  struct vfsmount *);
 extern void kern_unmount_array(struct vfsmount *mnt[], unsigned int num);
 
+extern int cifs_root_data(char **dev, char **opts);
+
 #endif /* _LINUX_MOUNT_H */

init/do_mounts.c

@@ -489,8 +489,6 @@ static int __init mount_nfs_root(void)
 
 #ifdef CONFIG_CIFS_ROOT
 
-extern int cifs_root_data(char **dev, char **opts);
-
 #define CIFSROOT_TIMEOUT_MIN	5
 #define CIFSROOT_TIMEOUT_MAX	30
 #define CIFSROOT_RETRY_MAX	5