s3: vfs: shadow_copy2: Replace all uses of (p-name) with len_before_gmt.

s3: vfs: shadow_copy2: Replace all uses of (p-name) with len_before_gmt.

p and name don't change, and we've already calculated this length.
Part of the effort to make the code inside vfs_snapper.c that does
the same thing more similar (we can't make these functions identical
due to the 'snapdir' use case).

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12150

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>