Documentation/kcov: Define `ip' in the example.

The example code uses the variable `ip' but never declares it.

Declare `ip' as a 64bit variable which is the same type as the array
from which it loads its value.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20210830172627.267989-3-bigeasy@linutronix.de

Documentation/dev-tools/kcov.rst

@@ -178,6 +178,8 @@ Comparison operands collection is similar to coverage collection:
 	/* Read number of comparisons collected. */
 	n = __atomic_load_n(&cover[0], __ATOMIC_RELAXED);
 	for (i = 0; i < n; i++) {
+		uint64_t ip;
+
 		type = cover[i * KCOV_WORDS_PER_CMP + 1];
 		/* arg1 and arg2 - operands of the comparison. */
 		arg1 = cover[i * KCOV_WORDS_PER_CMP + 2];