sysutils/devcpu-data-amd: Unbreak & fix syntax error

when PORTREVISION=0 && MASTER_SITE_FREEBSD=yes.

make[4]: "/usr/ports/Mk/bsd.port.mk" line 2505: Unclosed variable "/"
make[4]: "/usr/ports/Mk/bsd.port.mk" line 2505: Undefined variable "${/"
make[4]: Fatal errors encountered -- cannot continue===> sysutils/devcpu-data-amd failed
*** [describe.sysutils] Error code 1

I don't see any reasons to use per-version DIST_SUBDIR since it causes
Makefile syntax error and distfiles now includes its revision hash like this:

 - microcode_amd.bin?id=f5d519563ac9d2d1f382a817aae5ec5473811ac

Approved by:	portmgr (build fix blanket)