xprtrdma: Rename frwr_release_mr()

[ Upstream commit f912af77 ]

Clean up: To be consistent with other functions in this source file,
follow the naming convention of putting the object being acted upon
before the action itself.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Stable-dep-of: acd9f2dd ("xprtrdma: Fix rpcrdma_reqs_reset()")
Signed-off-by: Sasha Levin <sashal@kernel.org>