block/snapshot: Fix compiler warning with -Wshadow=local

block/snapshot: Fix compiler warning with -Wshadow=local

No need to declare a new variable in the the inner code block
here, we can re-use the "ret" variable that has been declared
at the beginning of the function. With this change, the code
can now be successfully compiled with -Wshadow=local again.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20231023175038.111607-1-thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>