sparc64: Fix prototype warning for init_vdso_image

Fix the following warning:
arch/sparc/vdso/vma.c:246:12: warning: no previous prototype for ‘init_vdso_image’

init_vdso_image has no users outside vma.c, make it static.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: David S. Miller <davem@davemloft.net>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20240330-sparc64-warnings-v1-1-37201023ee2f@ravnborg.orgSigned-off-by: Andreas Larsson <andreas@gaisler.com>

arch/sparc/vdso/vma.c

@@ -243,8 +243,9 @@ static int stick_patch(const struct vdso_image *image, struct vdso_elfinfo *e, b
  * Allocate pages for the vdso and vvar, and copy in the vdso text from the
  * kernel image.
  */
-int __init init_vdso_image(const struct vdso_image *image,
-			   struct vm_special_mapping *vdso_mapping, bool elf64)
+static int __init init_vdso_image(const struct vdso_image *image,
+				  struct vm_special_mapping *vdso_mapping,
+				  bool elf64)
 {
 	int cnpages = (image->size) / PAGE_SIZE;
 	struct page *dp, **dpp = NULL;