If setting the printk log buffer (with the boot command line option
"log_buf_len") to a value that's not a power of two, the index calculations
go wrong and yield confusing results.

This patch rounds the size to the next higher power of two.  It'll yield
garbage for sizes > INT_MAX bytes.
Signed-off-by: Werner Almesberger <werner@almesberger.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>