Linux 5.14 compat: explicity assign set_page_dirty

Kernel 5.14 introduced a change where set_page_dirty of
struct address_space_operations is no longer implicitly set to
__set_page_dirty_buffers(), which ended up resulting in a NULL
pointer deref in the kernel when it is attempted to be called.
This change sets .set_page_dirty in the structure to
__set_page_dirty_nobuffers(), which was introduced with the
related patch set. The breaking change was introduce in commit
0af573780b0b13fceb7fabd49dc1b073cee9a507 to torvalds/linux.git.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #12427

module/os/linux/zfs/zpl_file.c

@@ -33,6 +33,9 @@
 #include <sys/zfs_vfsops.h>
 #include <sys/zfs_vnops.h>
 #include <sys/zfs_project.h>
+#ifdef HAVE_VFS_SET_PAGE_DIRTY_NOBUFFERS
+#include <linux/pagemap.h>
+#endif
 
 /*
  * When using fallocate(2) to preallocate space, inflate the requested
@@ -1018,6 +1021,9 @@ const struct address_space_operations zpl_address_space_operations = {
 	.writepage	= zpl_writepage,
 	.writepages	= zpl_writepages,
 	.direct_IO	= zpl_direct_IO,
+#ifdef HAVE_VFS_SET_PAGE_DIRTY_NOBUFFERS
+	.set_page_dirty = __set_page_dirty_nobuffers,
+#endif
 };
 
 const struct file_operations zpl_file_operations = {