staging: exfat: fix multiple definition error of `rename_file'

`rename_file' was exported but not properly namespaced causing a
multiple definition error because `rename_file' is already defined in
fs/hostfs/hostfs_user.c:

ld: drivers/staging/exfat/exfat_core.o: in function `rename_file':
drivers/staging/exfat/exfat_core.c:2327: multiple definition of
`rename_file'; fs/hostfs/hostfs_user.o:fs/hostfs/hostfs_user.c:350:
first defined here
make: *** [Makefile:1077: vmlinux] Error 1

This error can be reproduced on ARCH=um by selecting:

CONFIG_EXFAT_FS=y
CONFIG_HOSTFS=y

Add a namespace prefix exfat_* to fix this error.
Reported-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Cc: stable <stable@vger.kernel.org>
Cc: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/r/20191204234522.42855-1-brendanhiggins@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/exfat/exfat.h

@@ -805,8 +805,8 @@ s32 create_dir(struct inode *inode, struct chain_t *p_dir,
 s32 create_file(struct inode *inode, struct chain_t *p_dir,
 		struct uni_name_t *p_uniname, u8 mode, struct file_id_t *fid);
 void remove_file(struct inode *inode, struct chain_t *p_dir, s32 entry);
-s32 rename_file(struct inode *inode, struct chain_t *p_dir, s32 old_entry,
-		struct uni_name_t *p_uniname, struct file_id_t *fid);
+s32 exfat_rename_file(struct inode *inode, struct chain_t *p_dir, s32 old_entry,
+		      struct uni_name_t *p_uniname, struct file_id_t *fid);
 s32 move_file(struct inode *inode, struct chain_t *p_olddir, s32 oldentry,
 	      struct chain_t *p_newdir, struct uni_name_t *p_uniname,
 	      struct file_id_t *fid);

drivers/staging/exfat/exfat_core.c

@@ -2324,8 +2324,8 @@ void remove_file(struct inode *inode, struct chain_t *p_dir, s32 entry)
 	fs_func->delete_dir_entry(sb, p_dir, entry, 0, num_entries);
 }
 
-s32 rename_file(struct inode *inode, struct chain_t *p_dir, s32 oldentry,
-		struct uni_name_t *p_uniname, struct file_id_t *fid)
+s32 exfat_rename_file(struct inode *inode, struct chain_t *p_dir, s32 oldentry,
+		      struct uni_name_t *p_uniname, struct file_id_t *fid)
 {
 	s32 ret, newentry = -1, num_old_entries, num_new_entries;
 	sector_t sector_old, sector_new;

drivers/staging/exfat/exfat_super.c

@@ -1262,8 +1262,8 @@ static int ffsMoveFile(struct inode *old_parent_inode, struct file_id_t *fid,
 	fs_set_vol_flags(sb, VOL_DIRTY);
 
 	if (olddir.dir == newdir.dir)
-		ret = rename_file(new_parent_inode, &olddir, dentry, &uni_name,
-				  fid);
+		ret = exfat_rename_file(new_parent_inode, &olddir, dentry,
+					&uni_name, fid);
 	else
 		ret = move_file(new_parent_inode, &olddir, dentry, &newdir,
 				&uni_name, fid);