blktrace: really fix parallel build issue

Fixes:
http://autobuild.buildroot.net/results/dd4/dd47b3ca17bdb597d6b12de6b381cf5f25abaf71/
http://autobuild.buildroot.net/results/a84/a842234fbdc8f65d48089b90ee23523540a7091f/
http://autobuild.buildroot.net/results/e63/e6351692ad6aef397e68ffdf107f3a85e4490015/



And many more.

Commit a21163ae (package/blktrace: do not build in parallel) tried to fix
the parallel build issue, but the package doesn't use the autotools package
infrastructure so BLKTRACE_MAKE isn't used.  Instead replace the explicit
$(MAKE) calls with $(MAKE1).

Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>