pvmfw: helpers: Represent addresses as usize

Use the more natural type to represent "pointers as integers".

Test: -
Change-Id: I9bedfb1aad80769f5b3beaf18e896226c09ba758
diff --git a/pvmfw/src/exceptions.rs b/pvmfw/src/exceptions.rs
index 0fb2911..03fc220 100644
--- a/pvmfw/src/exceptions.rs
+++ b/pvmfw/src/exceptions.rs
@@ -20,14 +20,14 @@
 use vmbase::{console::emergency_write_str, eprintln, power::reboot};
 
 const ESR_32BIT_EXT_DABT: u64 = 0x96000010;
-const UART_PAGE: u64 = page_4kb_of(console::BASE_ADDRESS as u64);
+const UART_PAGE: usize = page_4kb_of(console::BASE_ADDRESS);
 
 #[no_mangle]
 extern "C" fn sync_exception_current(_elr: u64, _spsr: u64) {
     let esr = read_esr();
     let far = read_far();
     // Don't print to the UART if we're handling the exception it could raise.
-    if esr != ESR_32BIT_EXT_DABT || page_4kb_of(far) != UART_PAGE {
+    if esr != ESR_32BIT_EXT_DABT || page_4kb_of(far as usize) != UART_PAGE {
         emergency_write_str("sync_exception_current\n");
         print_esr(esr);
     }