fix(spmd): error macro to use correct print format

Following merge of [1] then [2] broke the build because of an incorrect
format specifier in an ERROR macro. Fix to use the correct print format.

[1] https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/5437
[2] https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/9211

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I14d4c31091f6a5f4c3252f6d810e9d2bb2f545c4
1 file changed