ARM: 7379/1: DT: fix atags_to_fdt() second call site

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: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>