rbtree: optimize rb_erase()

rbtree: optimize rb_erase()

Tfour 4 redundant if-conditions in function __rb_erase_color() in
lib/rbtree.c are removed.

In pseudo-source-code, the structure of the code is as follows:

if ((!A || B) && (!C || D)) {
.
.
.
} else {
		if (!C || D) {//if this is true, it implies: (A == true) && (B == false)
				if (A) {//hence this always evaluates to 'true'...
						.
				}
				.
				//at this point, C always becomes true, because of:
				__rb_rotate_right/left();
				//and:
				other = parent->rb_right/left;
		}
		.
		.
		if (C) {//...and this too !
				.
		}
}

Signed-off-by: Wolfram Strepp <wstrepp@gmx.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[Linux commit 55a63998b8967615a15e2211ba0ff3a84a565824]

Ported to Xen.

Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>