libc/uclibc: fix src dir location

Now that we akways extract the tarballs in a sane location (see changeset
#6e1412ba8da9: scripts/functions: force extract folder to archive basename),
the uClibc snapshot dir now has the date (as version) in it, eg.:
uClibc-20100710

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Remy Bohmer"

 reporter_url="linux@bohmer.net"

 reporter_comment="Example for building a toolchain for m68000 bare metal targets"