erofs: Replace zero-length array with flexible-array member

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.

Kernel code should always use `flexible array members' [1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used [2].

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.15/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://lore.kernel.org/r/20211206121702.221331-1-hsiangkao@linux.alibaba.comReported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/erofs_fs.h

@@ -209,7 +209,7 @@ struct erofs_xattr_ibody_header {
 	__le32 h_reserved;
 	__u8   h_shared_count;
 	__u8   h_reserved2[7];
-	__le32 h_shared_xattrs[0];      /* shared xattr id array */
+	__le32 h_shared_xattrs[];       /* shared xattr id array */
 };
 
 /* Name indexes */
@@ -226,7 +226,7 @@ struct erofs_xattr_entry {
 	__u8   e_name_index;    /* attribute name index */
 	__le16 e_value_size;    /* size of attribute value */
 	/* followed by e_name and e_value */
-	char   e_name[0];       /* attribute name */
+	char   e_name[];        /* attribute name */
 };
 
 static inline unsigned int erofs_xattr_ibody_size(__le16 i_xattr_icount)