xen/riscv: fix type mismatch in read_atomic_size()

Correct a typo in read_atomic_size() where a 64-bit result
was incorrectly cast to a `uint32_t` instead of `uint64_t`
in the case of 8-byte reads.

Fixes: 3cd46d4 ("xen/riscv: introduce atomic.h")
Reported-by: Andrew Cooper <[email protected]>
Signed-off-by: Oleksii Kurochko <[email protected]>
Reviewed-by: Jan Beulich <[email protected]>

xen/arch/riscv/include/asm/atomic.h

@@ -45,7 +45,7 @@ static always_inline void read_atomic_size(const volatile void *p,
     case 2: *(uint16_t *)res = readw(p); break;
     case 4: *(uint32_t *)res = readl(p); break;
 #ifndef CONFIG_RISCV_32
-    case 8: *(uint32_t *)res = readq(p); break;
+    case 8: *(uint64_t *)res = readq(p); break;
 #endif
     default: __bad_atomic_size(); break;
     }