ipmi: work around gcc-4.9 build warning

Building ipmi on arm with gcc-4.9 results in this warning for an
allmodconfig build:

  drivers/char/ipmi/ipmi_si_intf.c: In function 'ipmi_thread':
  include/linux/time.h:28:5: warning: 'busy_until.tv_sec' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if (lhs->tv_sec > rhs->tv_sec)
       ^
  drivers/char/ipmi/ipmi_si_intf.c:1007:18: note: 'busy_until.tv_sec' was declared here
    struct timespec busy_until;
                    ^

The warning is bogus and this case can not occur.  Apparently this is a
false positive resulting from gcc getting a little smarter about
tracking assignments but not smart enough.

Marking the ipmi_thread_busy_wait function as inline gives the gcc
optimization logic enough information to figure out for itself that the
case cannot happen, which gets rid of the warning without adding any
fake initialization.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>