set_sbat_uefi_variable(): align some decisions that are off-by-one.

Fix a couple of small off-by-one errors in the SBAT variable initial
setup and validation path.

Signed-off-by: Peter Jones <pjones@redhat.com>

sbat.c

@@ -324,8 +324,8 @@ set_sbat_uefi_variable(void)
  if (EFI_ERROR(efi_status)) {
  dprint(L"SBAT read failed %r\n", efi_status);
  } else if (check_sbat_var_attributes(attributes) &&
-   sbatsize >= strlen(SBAT_VAR_SIG "1") &&
-   strncmp((const char *)sbat, SBAT_VAR_SIG,
+   sbatsize >= strlen(SBAT_VAR_SIG "1") &&
+   strncmp((const char *)sbat, SBAT_VAR_SIG,
  strlen(SBAT_VAR_SIG))) {
  dprint("SBAT variable is %d bytes, attributes are 0x%08x\n",
  sbatsize, attributes);
@@ -348,7 +348,7 @@ set_sbat_uefi_variable(void)
 
  /* set variable */
  efi_status = set_variable(SBAT_VAR_NAME, SHIM_LOCK_GUID, SBAT_VAR_ATTRS,
- sizeof(SBAT_VAR), SBAT_VAR);
+ sizeof(SBAT_VAR)-1, SBAT_VAR);
  if (EFI_ERROR(efi_status)) {
  dprint(L"SBAT variable writing failed %r\n", efi_status);
  return efi_status;