Work around a possible bug in the FRV compiler.

What appears to be happening is that gcc resolves the
__builtin_constant_p() in kmalloc() to true, but then fails to reduce the
therefore constant conditions in the if-statements it guards to constant
results.

When compiling with -O2 or -Os, one single spurious error crops up in
cpuup_callback() in mm/slab.c.  This can be avoided by making the memsize
variable const.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>