xfs: move the xfs_attr_sf_lookup tracepoint

trace_xfs_attr_sf_lookup is currently only called by
xfs_attr_shortform_lookup, which despit it's name is a simple helper for
xfs_attr_shortform_addname, which has it's own tracing.  Move the
callsite to xfs_attr_shortform_getvalue, which is the closest thing to
a high level lookup we have for the Linux xattr API.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>