If you try to stop the ASM using srvctl without the -f option most likely you get the same error.
or maybe you can stop it using sqlplus, but i like using srvctl specially if its clustered.
$ srvctl stop asm
PRCR-1065 : Failed to stop resource ora.asm CRS-2529: Unable to act on 'ora.asm' because that would require stopping or relocating 'ora.DATA.dg', but the force option was not specified
Add -f (mean force) to the stop command
$ srvctl stop asm -f
Now check the ASM
$ srvctl status asm ASM is not running. $