fs/inode.c: inode_set_flags(): replace opencoded set_mask_bits()

It seems that commits 5f16f3225b0624 and 00a1a053ebe5, both with same
commitlog ("ext4: atomically set inode->i_flags in ext4_set_inode_flags()")
introduced the set_mask_bits API, but somehow missed not using it in ext4
in the end.

Also, set_mask_bits() is used in fs quite a bit and we can possibly come
up with a generic llsc based implementation (w/o the cmpxchg loop)

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Vineet Gupta <[e-mail]>
Reviewed-by: Anthony Yznaga <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Theodore Ts'o <[e-mail]>
Cc: Peter Zijlstra (Intel) <[e-mail]>
Cc: Chris Wilson <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Miklos Szeredi <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/inode.c

···
 void inode_set_flags(struct inode *inode, unsigned int flags,
 		     unsigned int mask)
 {
-	unsigned int old_flags, new_flags;
-
 	WARN_ON_ONCE(flags & ~mask);
-	do {
-		old_flags = READ_ONCE(inode->i_flags);
-		new_flags = (old_flags & ~mask) | flags;
-	} while (unlikely(cmpxchg(&inode->i_flags, old_flags,
-				  new_flags) != old_flags));
+	set_mask_bits(&inode->i_flags, mask, flags);
 }
 EXPORT_SYMBOL(inode_set_flags);