powerpc/44x: Fix mask and shift to zero bug

commit 8d046759f6ad75824fdf7b9c9a3da0272ea9ea92 upstream.

My static checker complains that 0x00001800 >> 13 is zero. Looking at
the context, it seems like a copy and paste bug from the line below
and probably 0x3 << 13 or 0x00006000 was intended.

Fixes: 2af59f7d5c3e ("[POWERPC] 4xx: Add 405GPr and 405EP support in boot wrapper")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>