loader: fix mismatched type for inline assembly

[KurtWu10]

This fixes the following warning when using the llvm toolchain

src/aarch64/init.c:140:45: error: value size does not match register size specified by the constraint and modifier [-Werror,-Wasm-operand-widths]
  140 |     asm volatile("msr TPIDR_EL1, %0" :: "r"(logical_cpu));
      |                                             ^
src/aarch64/init.c:140:34: note: use constraint modifier "w"
  140 |     asm volatile("msr TPIDR_EL1, %0" :: "r"(logical_cpu));
      |                                  ^~
      |                                  %w0
1 error generated.

[Ivan-Velickovic]

Thanks, I noticed that recently but forgot to fix.