iomap: remove set_memor_ro() on zero page

Stephen reported a boot failure on ppc power8 system where
set_memor_ro() on the new zero page failed [0]. Christophe Leroy
further clarifies we can't use this on on linear memory on ppc, and
so instead of special casing this just for PowerPC [2] remove the
call as suggested by Darrick.

[0] https://lore.kernel.org/all/[e-mail]/T/#u
[1] https://lore.kernel.org/all/[e-mail]/
[2] https://lore.kernel.org/all/[e-mail]/

Reported-by: Stephen Rothwell <[e-mail]>
Suggested-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Luis Chamberlain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Tested-by: Stephen Rothwell <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

fs/iomap/direct-io.c

···
 #include <linux/iomap.h>
 #include <linux/backing-dev.h>
 #include <linux/uio.h>
-#include <linux/set_memory.h>
 #include <linux/task_io_accounting_ops.h>
 #include "trace.h"
 
···
 	if (!zero_page)
 		return -ENOMEM;
 
-	set_memory_ro((unsigned long)page_address(zero_page),
-		      1U << IOMAP_ZERO_PAGE_ORDER);
 	return 0;
 }
 fs_initcall(iomap_dio_init);