We need to write new value if the bit mask fields of new value is not
equal to old value.  It does not make sense to write new value only when
all the bit_mask bits are zero.
Signed-off-by: NAxel Lin <axel.lin@gmail.com>
Cc: Michael Hennerich <michael.hennerich@analog.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>