scsi_proc: make proc_scsi_host_open() preallocate a bigger buffer

Some of the ->show_info() instances really spew a lot; it's not a problem
wrt correctness (seq_read() will grow buffer and call the sucker again),
but in this case it makes sense to start with a somewhat bigger one -
they often do exceed one page worth of output.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>