drm/nouveau/bios: fix a bit shift error introduced by 457e77b

Commit 457e77b added two checks applied to a
value received from nv_rd32(bios, 0x619f04). But after this new piece of code
is executed, the addr local variable does not hold the same value it used to
hold before the commit. Here is what is was assigned in the original code:
	(u64)(nv_rd32(bios, 0x619f04) & 0xffffff00) << 8
in the committed code it ends up with this value:
	(u64)(nv_rd32(bios, 0x619f04) >> 8) << 8
These expressions are obviously not equivalent.

My Nvidia video card does not show anything on the display when I boot a
kernel containing this commit.

The patch fixes the code so that the new checks are still done, but the
side effect of an incorrect addr value is gone.

Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sergei Antonov <saproj@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/core/subdev/bios/base.c

@@ -109,7 +109,7 @@ nouveau_bios_shadow_pramin(struct nouveau_bios *bios)
 			return;
 		}
 
-		addr = (u64)(addr >> 8) << 8;
+		addr = (addr & 0xffffff00) << 8;
 		if (!addr) {
 			addr  = (u64)nv_rd32(bios, 0x001700) << 16;
 			addr += 0xf0000;