utils: fix toolchains path typo rel1 -> Rel1

The archive is extracted as arm-gnu-toolchain-13.2.Rel1-*, not with rel1. Because of this, we have the following build error:

make: aarch64-none-linux-gnu-gcc: No such file or directory

Fix the typo to fix the build error

Signed-off-by: Mattijs Korpershoek mkorpershoek@baylibre.com