bloom: remove a misleading const qualifier

bloom: remove a misleading const qualifier

When building with glibc-2.43 there is the following warning:

    bloom.c: In function ‘get_or_compute_bloom_filter’:
    bloom.c:515:52: warning: initialization discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
      515 |                                 char *last_slash = strrchr(path, '/');
          |                                                    ^~~~~~~

In this case, we always write through "path" through the "last_slash"
pointer. Therefore, the const qualifier on "path" is misleading and we
can just remove it.

Signed-off-by: Collin Funk <collin.funk1@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>