Fix type mismatch in sftp_find_request

Fix type mismatch in sftp_find_request

The id member of the sftp_request structure is of type unsigned int.
This type is also used in the sftp_reqfind callback. In
sftp_find_request we thus need to pass a pointer to unsigned int to
find234. Before this commit, sftp_find_request was passing a pointer
to unsigned long to find234, which causes the lookup to fail on
big-endian platforms where sizeof(unsigned int) != sizeof(unsigned
long), e.g. ppc64.