dm: Fix typo in error message

Remove the redundant "i" at the beginning of the error message. This "i"
came from commit 1c131886 ("dm: prefer
'"%s...", __func__'"), the "i" is accidentally left.

Signed-off-by: Ssuhung Yeh <ssuhung@gmail.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: 1c131886 ("dm: prefer '"%s...", __func__'")
Cc: stable@vger.kernel.org	# v6.3+