libsha1: add .hash file
Fixes:
http://autobuild.buildroot.org/results/e6d/e6d539a2c47428d1af2529069297af1279c8345f/
Similar to jquery-keyboard, it seems the libsha1 tarball on the autobuilder
is corrupt. Fix it by adding a .hash file so it falls back to our s.b.o
mirror.
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>