oprofile: fix oops on x86 32-bit

x86 32-bit isn't saving the stack pointer to pt_regs->esp when an
interrupt occurs.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Tested-by: Robert Fitzsimons <robfitz@273k.net>
Cc: Andi Kleen <ak@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Philippe Elie <phil.el@wanadoo.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>