ARM: bcm2835: Fix integer overflow in rpi_firmware_print_firmware_revision()

time64_t is 64-bit width type, we are not supposed to supply lesser ones
as in the case of rpi_firmware_print_firmware_revision() after the commit
4a60f58e ("ARM: bcm2835: Switch to use %ptT"). Use temporary variable
of time64_t type to correctly handle lesser types.

Fixes: 4a60f58e ("ARM: bcm2835: Switch to use %ptT")
Reported-by: Stefan Wahren <wahrenst@gmx.net>
Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Revieved-by: Petr Mladek <pmladek@suse.com>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Link: https://lore.kernel.org/r/20200616163139.4229-1-andriy.shevchenko@linux.intel.com