powerpc/ps3: Fix system hang with GCC 5 builds

[ Upstream commit 6dff5b67054e17c91bd630bcdda17cfca5aa4215 ]

GCC 5 generates different code for this bootwrapper null check that
causes the PS3 to hang very early in its bootup. This check is of
limited value, so just get rid of it.

Cc: stable@vger.kernel.org
Signed-off-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>