common/board_r: remove warning in initr_mem for 64-bit phys_size_t

Since on powerpc phys_size_t can be unsigned long long, this printout
line can result in a not nice compile warning.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Acked-by: Simon Glass <sjg@chromium.org>

common/board_r.c

@@ -664,7 +664,7 @@ int initr_mem(void)
 	/* Also take the logbuffer into account (pram is in kB) */
 	pram += (LOGBUFF_LEN + LOGBUFF_OVERHEAD) / 1024;
 # endif
-	sprintf(memsz, "%ldk", (gd->ram_size / 1024) - pram);
+	sprintf(memsz, "%ldk", (long int) ((gd->ram_size / 1024) - pram));
 	setenv("mem", memsz);
 
 	return 0;