cbmem_top_chipset: Change the return value to uintptr_t

Get rid of a lot of casts.

Change-Id: I93645ef5dd270905ce421e68e342aff4c331eae6
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69078
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jakub Czapiga <jacz@semihalf.com>

tests/lib/coreboot_table-test.c

@@ -243,9 +243,9 @@ void cbmem_run_init_hooks(int is_recovery)
 }
 
 extern uintptr_t _cbmem_top_ptr;
-void *cbmem_top_chipset(void)
+uintptr_t cbmem_top_chipset(void)
 {
-	return (void *)_cbmem_top_ptr;
+	return _cbmem_top_ptr;
 }
 
 #define CBMEM_SIZE (64 * KiB)