linux: Make sure that config file is closed after editing is done
linux: Make sure that config file is closed after editing is done

Fixes warnings with python3

WARNING: /a/builder/home/kraj/work/oe/meta-gumstix-community/recipes-kernel/linux/linux-omap-3.5.bb: <string>:15:
 ResourceWarning: unclosed file <_io.TextIOWrapper name='/a/builder/home/kraj/work/oe/meta-gumstix-community/reci
pes-kernel/linux/linux-omap-3.5/overo/defconfig' mode='r' encoding='UTF-8'>

Signed-off-by: Khem Raj <729d64b6f67515e258459a5f6d20ec88b2caf8df@gmail.com>

schnitzeltony/meta-gumstix-community,schnitzeltony/meta-gumstix-community