It was pointed out in review of the previous patch that the if leg
isn't needed as the for loop will not enter on an empty $device_archs.

Fixes: d1d5e9ee

 ("configure: allow the selection of alternate config in the build")
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210720232703.10650-5-alex.bennee@linaro.org>