lockdep: fix compilation when CONFIG_TRACE_IRQFLAGS_SUPPORT is not set

This patch fixes compilation if CONFIG_TRACE_IRQFLAGS_SUPPORT is ever
disabled (which is currently not allowed by Kconfig). Alternatively
we could just remove the option altogether and the associated code
paths. Since the compilation error has been in the tree for at
least two years and no one noticed it, I guess we don't really have
the need for CONFIG_TRACE_IRQFLAGS_SUPPORT=n.

Boot tested on x86 UP.

Signed-off-by: Rui Sousa <rui.p.m.sousa@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>