smb3: rc uninitialized in one fallocate path

stable inclusion
from stable-5.10.58
commit c8b7cfa674ee18dcef601427c07aad987e4195a3
bugzilla: 176984 https://gitee.com/openeuler/kernel/issues/I4E2P4

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8b7cfa674ee18dcef601427c07aad987e4195a3



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[ Upstream commit 5ad4df56 ]

Clang detected a problem with rc possibly being unitialized
(when length is zero) in a recently added fallocate code path.

Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>