fbdev/ps3fb: fix compile warning

Commit 11bd5933 ("fbdev/ps3fb: use vm_iomap_memory()") introduced
the following warning:

drivers/video/ps3fb.c: In function 'ps3fb_mmap':
drivers/video/ps3fb.c:712:2: warning: suggest parentheses around '+' inside '<<' [-Wparentheses]

Fix this by adding the parentheses.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/ps3fb.c

@@ -710,7 +710,7 @@ static int ps3fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
 	r = vm_iomap_memory(vma, info->fix.smem_start, info->fix.smem_len);
 
 	dev_dbg(info->device, "ps3fb: mmap framebuffer P(%lx)->V(%lx)\n",
-		info->fix.smem_start + vma->vm_pgoff << PAGE_SHIFT,
+		info->fix.smem_start + (vma->vm_pgoff << PAGE_SHIFT),
 		vma->vm_start);
 
 	return r;