arch: Address Rust 1.51.0 clippy issue (upper_case_acronyms)

error: name `RSDPPastRamEnd` contains a capitalized acronym
  --> arch/src/lib.rs:59:5
   |
59 |     RSDPPastRamEnd,
   |     ^^^^^^^^^^^^^^ help: consider making the acronym lowercase, except the initial letter: `RsdpPastRamEnd`
   |
   = note: `-D clippy::upper-case-acronyms` implied by `-D warnings`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#upper_case_acronyms

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

arch/src/lib.rs

@@ -56,7 +56,7 @@ pub enum Error {
     /// Error writing module entry to guest memory.
     ModlistSetup(vm_memory::GuestMemoryError),
     /// RSDP Beyond Guest Memory
-    RSDPPastRamEnd,
+    RsdpPastRamEnd,
 }
 
 /// Type for returning public functions outcome.