Fix warnings for page_header_get_field() comparisons

The type uint16_t is apparently promoted to int in a comparison,
causing a sign mismatch when comparing to ulint. Convert to ulint
before comparison.

storage/innobase/page/page0page.cc

@@ -2117,7 +2117,7 @@ page_simple_validate_old(
 		goto func_exit;
 	}
 
-	if (UNIV_UNLIKELY(page_header_get_field(page, PAGE_N_RECS)
+	if (UNIV_UNLIKELY(ulint(page_header_get_field(page, PAGE_N_RECS))
 			  + PAGE_HEAP_NO_USER_LOW
 			  != count + 1)) {
 		ib::error() <<  "n recs wrong "
@@ -2308,7 +2308,7 @@ page_simple_validate_new(
 		goto func_exit;
 	}
 
-	if (UNIV_UNLIKELY(page_header_get_field(page, PAGE_N_RECS)
+	if (UNIV_UNLIKELY(ulint(page_header_get_field(page, PAGE_N_RECS))
 			  + PAGE_HEAP_NO_USER_LOW
 			  != count + 1)) {
 		ib::error() << "n recs wrong "