Fix clang compilation on aarch64: sizeof operator error.

Fix clang compilation on aarch64: sizeof operator error.

Fixes clang error: argument to 'sizeof' in 'memcpy' call is the same
pointer type 'unformat_input_t *' (aka 'struct _unformat_input_t *')
as the source; expected 'unformat_input_t' (aka 'struct
_unformat_input_t') or an explicit length.

Change-Id: If00303343b10fe1732e477549727a41445edf410
Signed-off-by: Sirshak Das <sirshak.das@arm.com>
Reviewed-by: Brian Brooks <brian.brooks@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>