<linux/kernel.h>: drop the gcc-3.3 'const' hack in roundup()

<linux/kernel.h>: drop the gcc-3.3 'const' hack in roundup()

The single quotation marks around "const" were causing a documentation
markup warning with reST.  Instead of fixing that warning, just delete
that comment line and the gcc-3.3 hack of using "const" in the roundup()
macro since gcc-3.3 is no longer supported for kernel builds.

I did around 20 different $arch builds with no problems, but we'll just
have to see if this causes problems for anyone else out there.

Link: http://lkml.kernel.org/r/ec5dcf72-7c3e-3513-af0c-4003ed598854@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>