${FAMILY} might be undefined and should be enclosed in quotes.
Maintainer informed via mail
Created attachment 226531 [details] Patch for sysutils/u-boot-master/Makefile adding quotation marks around ${FAMILY}
How to repeat (on bare metal amd64): make -C /usr/ports/sysutils/u-boot-master -V FAMILY -V OPSYS -V OSVERSION
Commit 395942b1e221ae6ae056add36a7c39d186b0faa4 solved the issue using another method.