swupdate-common: fix sha256 regex
swupdate-common: fix sha256 regex

Change sha256 regex brackets to parenthesis to apply only on line with 'sha256'
and 'version'.

Signed-off-by: Louis Rannou <7b6c153ec89c01d1d352c6940285496c822b2fbd@gresille.org>

sbabic/meta-swupdate,sbabic/meta-swupdate