toolchain-external: fix Linaro ARM URL

Commit 79828fc0 (toolchain-external:
update ARM Linaro toolchains) accidently broke the URL for the Linaro
2013.01 toolchain by replacing a .bz2 extension by .bz. This patch
fixes this problem.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>