Well, changing that message might not be possible (or maybe). I can recommend you to rename the device name using dmsetup command.
Warning: Do not run these commands without understanding them. A simple mistake will boot your system to intitramfs.
Here goes a similar question (not exactly the same). It's solution will help you in renaming it to something else. How to change the name an encrypted full-system partition is mapped to
Here's a brief summary of commands that you might need from that guide.
sudo dmsetup rename /dev/mapper/sda1_crypt myhiddenname
sudo sed -i 's/sda1_crypt/myhiddenname/g' /etc/crypttab
sudo update-initramfs -u -k all
Note: Do not just copy paste above commands without understanding its parameters. You'll have to verify you're using correct deviice name and there's no typo.
Here, the first command will rename your crypt disk name. You can verify before and after change using lsblk. The second command will change the old name entry to new name in /etc/crypttab file which will tell the new encrypted disk name to be unlocked and the last command is to apply the changes you made in the /etc/crypttab file.
It is technically not changing the message. Instead you are renaming the the name of your crypt disk. If you just wanted to hide sda1 which represents your partition on your sda SATA device, then this solution will work.