ANDROID: staging: ion: Fix uninitialized variable warning

Warning:
   In file included from include/linux/bitops.h:19:0,
                    from include/linux/bitmap.h:8,
                    from drivers/staging/android/ion/ion.c:10:
   drivers/staging/android/ion/ion.c: In function '__ion_device_add_heap':
>> arch/m68k/include/asm/bitops.h:371:28: warning: 'end_bit' may be used uninitialized in this function [-Wmaybe-uninitialized]
    #define find_next_zero_bit find_next_zero_bit
                               ^~~~~~~~~~~~~~~~~~
   drivers/staging/android/ion/ion.c:228:17: note: 'end_bit' was declared here
     int start_bit, end_bit;
                    ^~~~~~~
   In file included from include/linux/bitops.h:19:0,
                    from include/linux/bitmap.h:8,
                    from drivers/staging/android/ion/ion.c:10:
>> arch/m68k/include/asm/bitops.h:354:10: warning: 'start_bit' may be used uninitialized in this function [-Wmaybe-uninitialized]
      offset -= bit;
      ~~~~~~~^~~~~~
   drivers/staging/android/ion/ion.c:228:6: note: 'start_bit' was declared here
     int start_bit, end_bit;
         ^~~~~~~~~

Change-Id: I2df4a5b36f457aca5f19c03976ae7229c35ecdb3
Reported-by: kbuild test robot <lkp@intel.com>
Fixes: acbfdf32 ("ANDROID: staging: ion: add support for consistent heap ids")
Signed-off-by: Sandeep Patil <sspatil@google.com>