airo: remove unused variables len and dev and clean up formatting

Variables len and dev assigned values but are never used hence they
are redundant and can be removed.  Also add in white space in for-loop
and remove some { } braces on if statement.

Cleans up clang warnings:
warning: variable 'len' set but not used [-Wunused-but-set-variable]
warning: variable 'dev' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>