s390/kexec: Fix checksum validation return code for kdump

Before kexec boots to a crash kernel it checks whether the image in memory
changed after load. This is done by the function kdump_csum_valid, which
returns true, i.e. an int != 0, on success and 0 otherwise. In other words
when kdump_csum_valid returns an error code it means that the validation
succeeded. This is not only counterintuitive but also produces the wrong
result if the kernel was build without CONFIG_CRASH_DUMP. Fix this by
making kdump_csum_valid return a bool.

Signed-off-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Acked-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/machine_kexec.c

@@ -144,7 +144,7 @@ static noinline void __machine_kdump(void *image)
 /*
  * Check if kdump checksums are valid: We call purgatory with parameter "0"
  */
-static int kdump_csum_valid(struct kimage *image)
+static bool kdump_csum_valid(struct kimage *image)
 {
 #ifdef CONFIG_CRASH_DUMP
 	int (*start_kdump)(int) = (void *)image->start;
@@ -153,9 +153,9 @@ static int kdump_csum_valid(struct kimage *image)
 	__arch_local_irq_stnsm(0xfb); /* disable DAT */
 	rc = start_kdump(0);
 	__arch_local_irq_stosm(0x04); /* enable DAT */
-	return rc ? 0 : -EINVAL;
+	return rc == 0;
 #else
-	return -EINVAL;
+	return false;
 #endif
 }