block: Keep bdrv_check*_request()'s return value

block: Keep bdrv_check*_request()'s return value

Do not throw away the value returned by bdrv_check_request() and
bdrv_check_byte_request().

Fix up some coding style issues in the proximity of the affected hunks.

Signed-off-by: Max Reitz <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Reviewed-by: Kevin Wolf <[email protected]>
Message-id: 1423162705[email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>