cros deploy: fix --unmerge

Make sure we pass a version qualifier when unmerging packages.
Tools do not accept a versioned atom unless there's an operator.

BUG=None
TEST=`cros deploy --unmerge screenshot` actually unmerges

Change-Id: I2f11883de3fdebac47e05f0026b4559e3ff44dfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2574019
Reviewed-by: Junichi Uekawa <uekawa@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/cli/deploy.py b/cli/deploy.py
index 74b8d6f..f343cc7 100644
--- a/cli/deploy.py
+++ b/cli/deploy.py
@@ -936,7 +936,7 @@
   if device.run(['qmerge', '--version'], check=False).returncode != 0:
     cmd = ['emerge']
 
-  cmd.extend(['--unmerge', pkg, '--root=%s' % root])
+  cmd.extend(['--unmerge', f'={pkg}', '--root=%s' % root])
   try:
     # Always showing the emerge output for clarity.
     device.run(cmd, capture_output=False, remote_sudo=True,