add-patch: use repository instance from add_i_state instead of the_repository

add-patch: use repository instance from add_i_state instead of the_repository

Functions parse_diff(), edit_hunk_manually() and patch_update_file() use
the_repository even though a repository instance is already available via
struct add_i_state s which is defined in struct add_p_state *s.

Use 's->s.r' instead of the_repository to avoid relying on global state. All
callers pass a valid add_p_state and this does not change any behavior.

This aligns with the ongoing effort to reduce usage of the_repository global
state.

Signed-off-by: Shreyansh Paliwal <redacted>
Signed-off-by: Junio C Hamano <redacted>