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>

src/include/cbmem.h

@@ -65,7 +65,7 @@ void *cbmem_top(void);
  * in the _cbmem_top_ptr symbol. Without CONFIG_RAMSTAGE_CBMEM_TOP_ARG the same
  * implementation as used in romstage will be used.
  */
-void *cbmem_top_chipset(void);
+uintptr_t cbmem_top_chipset(void);
 
 /* Add a cbmem entry of a given size and id. These return NULL on failure. The
  * add function performs a find first and do not check against the original