apply: only pass required data to find_name_*

apply: only pass required data to find_name_*

Currently the 'find_name_*()' functions take 'struct apply_state' as
parameter, even though they only need the 'root' member from that
struct.

These functions are in the callchain of 'parse_git_header()', which we
want to make more generally useful in a subsequent commit.  To make
that happen we only want to pass in the required data to
'parse_git_header()', and not the whole 'struct apply_state', and thus
we want functions in the callchain of 'parse_git_header()' to only
take arguments they really need.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>