aarch64: loader.ld: fix ELF initial program counter offset

mixed up 1000 with 0x1000. Went undetected since the linker
adjusts to a page anyway.
Spotted by the evil all-seeing eye of Paul Mundt.

Cc: Paul Mundt <paul.mundt@huawei.com>
Reviewed-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>