invalid value is not caught by the
validity check.  On the next context switch the broken fpc value will cause a
program check in the kernel.  Improving the checks in peek and poke fixes
this.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
n)+ח1x