staging: exfat: Use kvzalloc() instead of kzalloc() for exfat_sb_info

Fix mount failed "Cannot allocate memory".

When the memory gets fragmented, kzalloc() might fail to allocate
physically contiguous pages for the struct exfat_sb_info (its size is
about 34KiB) even the total free memory is enough.
Use kvzalloc() to solve this problem.
Reviewed-by: Ethan Wu <ethanwu@synology.com>
Signed-off-by: Jia-Ye Li <jiayeli@synology.com>
Link: https://lore.kernel.org/r/20190925083729.4653-1-jiayeli@synology.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/exfat/exfat_super.c

@@ -7,6 +7,7 @@
 #include <linux/init.h>
 #include <linux/time.h>
 #include <linux/slab.h>
+#include <linux/mm.h>
 #include <linux/seq_file.h>
 #include <linux/pagemap.h>
 #include <linux/mpage.h>
@@ -3450,7 +3451,7 @@ static void exfat_free_super(struct exfat_sb_info *sbi)
 		kfree(sbi->options.iocharset);
 	/* mutex_init is in exfat_fill_super function. only for 3.7+ */
 	mutex_destroy(&sbi->s_lock);
-	kfree(sbi);
+	kvfree(sbi);
 }
 
 static void exfat_put_super(struct super_block *sb)
@@ -3845,7 +3846,7 @@ static int exfat_fill_super(struct super_block *sb, void *data, int silent)
 	 * the filesystem, since we're only just about to mount
 	 * it and have no inodes etc active!
 	 */
-	sbi = kzalloc(sizeof(struct exfat_sb_info), GFP_KERNEL);
+	sbi = kvzalloc(sizeof(*sbi), GFP_KERNEL);
 	if (!sbi)
 		return -ENOMEM;
 	mutex_init(&sbi->s_lock);