fbdev/sgivwfb: fix compilation error in sgivwfb_mmap()

Commit c84deb9d615c02993ce0972a0b34585c7624822f ("fbdev/sgivwfb: use
vm_iomap_memory()") changed sgivwfb_mmap() to use the new
vm_iomap_memory() function. The commit introduced the following
compilation error:

drivers/video/sgivwfb.c:716:9: note: each undeclared identifier is
reported only once for each function it appears in

This patch fixes the error.

Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/video/sgivwfb.c

···
 	r = vm_iomap_memory(vma, sgivwfb_mem_phys, sgivwfb_mem_size);
 
 	printk(KERN_DEBUG "sgivwfb: mmap framebuffer P(%lx)->V(%lx)\n",
-	       offset, vma->vm_start);
+		sgivwfb_mem_phys + (vma->vm_pgoff << PAGE_SHIFT), vma->vm_start);
 
 	return r;
 }