Partially Revert "of: fix sparse warnings in fdt, irq, reserved mem, and resolver code"

A change to function pointers that was meant to address a sparse warning
turned out to cause hundreds of new gcc-7 warnings:

include/linux/of_irq.h:11:13: error: type qualifiers ignored on function return type [-Werror=ignored-qualifiers]
drivers/of/of_reserved_mem.c: In function '__reserved_mem_init_node':
drivers/of/of_reserved_mem.c:200:7: error: type qualifiers ignored on function return type [-Werror=ignored-qualifiers]
   int const (*initfn)(struct reserved_mem *rmem) = i->data;

Turns out the sparse warnings were spurious and have been fixed in
upstream sparse since 0.5.0 in commit "sparse: treat function pointers
as pointers to const data".

This partially reverts commit 17a70355ea576843a7ac851f1db26872a50b2850.

Fixes: 17a70355ea57 ("of: fix sparse warnings in fdt, irq, reserved mem, and resolver code")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/of_reserved_mem.c

@@ -197,7 +197,7 @@ static int __init __reserved_mem_init_node(struct reserved_mem *rmem)
 	const struct of_device_id *i;
 
 	for (i = __reservedmem_of_table; i < &__rmem_of_table_sentinel; i++) {
-		int const (*initfn)(struct reserved_mem *rmem) = i->data;
+		reservedmem_of_init_fn initfn = i->data;
 		const char *compat = i->compatible;
 
 		if (!of_flat_dt_is_compatible(rmem->fdt_node, compat))

include/linux/of_irq.h

@@ -8,7 +8,7 @@
 #include <linux/ioport.h>
 #include <linux/of.h>
 
-typedef int const (*of_irq_init_cb_t)(struct device_node *, struct device_node *);
+typedef int (*of_irq_init_cb_t)(struct device_node *, struct device_node *);
 
 /*
  * Workarounds only applied to 32bit powermac machines