mtd: maps: fix -Wvoid-pointer-to-enum-cast warning

When building with clang 18 I see the following warning:
| drivers/mtd/maps/physmap-versatile.c:209:25: warning: cast to smaller
| integer type 'enum versatile_flashprot' from 'const void *' [-Wvoid-pointer-to-enum-cast]
| 209 | versatile_flashprot = (enum versatile_flashprot)devid->data;

This is due to the fact that `devid->data` is a void* while `enum versatile_flashprot`
has the size of an int.

Cast `devid->data` to a uintptr_t to silence the above warning for clang
builds using W=1.

Link: https://github.com/ClangBuiltLinux/linux/issues/1910
Reported-by: Nathan Chancellor <[e-mail]>
Signed-off-by: Justin Stitt <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/20[e-mail]

drivers/mtd/maps/physmap-versatile.c

···
 		if (!sysnp)
 			return -ENODEV;
 
-		versatile_flashprot = (enum versatile_flashprot)devid->data;
+		versatile_flashprot = (uintptr_t)devid->data;
 		rmap = syscon_node_to_regmap(sysnp);
 		of_node_put(sysnp);
 		if (IS_ERR(rmap))