smb3: Improve exception handling in allocate_mr_list()

[ Upstream commit 96d566b6 ]

The kfree() function was called in one case by
the allocate_mr_list() function during error handling
even if the passed variable contained a null pointer.
This issue was detected by using the Coccinelle software.

Thus use another label.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>