ARM: fix build warning in proc-v7-bugs.c

The kernel test robot discovered that building without
HARDEN_BRANCH_PREDICTOR issues a warning due to a missing
argument to pr_info().

Add the missing argument.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 9dd78194 ("ARM: report Spectre v2 status through sysfs")
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>