atags_to_fdt() returns 1 when it fails to find a valid FDT signature.
The CONFIG_ARM_ATAG_DTB_COMPAT code is supposed to retry with another
location, but only does so when the initial call doesn't fail.

Fix this by using the correct condition in the assembly code.
Acked-by: NNicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>