checkkconfigsymbols.sh: Kconfig symbols sometimes have lowercase letters

checkkconfigsymbols.sh: Kconfig symbols sometimes have lowercase letters

Quite a few Kconfig symbols contain lowercase letters.  The current
checkkconfigsymbols.sh code only contains A-Z in the regexp it uses to
find config symbols in source code, so it comes up with the wrong symbol
to look for in Kconfig files and then generates false positives when it
doesn't find that wrong symbol.  For example checking drivers/net
generates a false positive for MAC89 because the the actual config
option is MAC89x0.

Fix this by also adding a-z to the regexp.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>