fwu: rename fwu_get_verified_mdata to fwu_get_mdata

fwu_get_mdata() sounds more appropriate than fwu_get_verified_mdata()

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Sughosh Ganu <sughosh.ganu@linaro.org>