elf_fdpic: fix unused variable warning

The elf_fdpic code shows a harmless warning when built with MMU disabled,
I ran into this now that fdpic is available on ARM randconfig builds
since commit 50b2b2e6 ("ARM: add ELF_FDPIC support").

fs/binfmt_elf_fdpic.c: In function 'elf_fdpic_dump_segments':
fs/binfmt_elf_fdpic.c:1501:17: error: unused variable 'addr' [-Werror=unused-variable]

This adds another #ifdef around the variable declaration to shut up
the warning.

Fixes: e6c1baa9 ("convert the rest of binfmt_elf_fdpic to dump_emit()")
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/binfmt_elf_fdpic.c

@@ -1489,7 +1489,9 @@ static bool elf_fdpic_dump_segments(struct coredump_params *cprm)
 	struct vm_area_struct *vma;
 
 	for (vma = current->mm->mmap; vma; vma = vma->vm_next) {
+#ifdef CONFIG_MMU
 		unsigned long addr;
+#endif
 
 		if (!maydump(vma, cprm->mm_flags))
 			continue;