tfa-next(next-checks-clippy): fix available platforms command

When calling `make -C rust list_platforms` to get the available
platforms of tfa-next, currently we are also saving the information
about make changing the directory and this gets confused with a new
platform to run clippy on.

 * Use make's --silent to silence the cd command and only get the
   listed platforms.

Change-Id: Ib8bb36c553e602837ec66770c65ba58c99e90a53
Signed-off-by: Tomás González <tomasagustin.gonzalezorlando@arm.com>
1 file changed