__printf() attributes help detecting issues in printf() format strings at
compile time.

Even though imr_selftest.c is only compiled with
CONFIG_DEBUG_IMR_SELFTEST=y, GCC complains about a missing format
attribute when compiling allmodconfig with -Wmissing-format-attribute.

Silence this warning by adding the attribute.
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Acked-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161219132144.4108-1-nicolas.iooss_linux@m4x.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>