Build: Fix applying patches to local library repo

The feature to force apply patches to local library repo actually
breaks.
Fix this feature by removing unnecessary ${} around force patch apply
config.
The same fix as that in commit [1].

[1] https://review.trustedfirmware.org/c/TF-M/trusted-firmware-m/+/23900

Signed-off-by: David Hu <david.hu@arm.com>
Change-Id: Ibc806c047492283c33eb49308bf6c4ace5e61dbc
1 file changed