arm64/scs: Fix potential sign extension issue of advance_loc4

arm64/scs: Fix potential sign extension issue of advance_loc4

The expression (*opcode++ << 24) and exp * code_alignment_factor
may overflow signed int and becomes negative.

Fix this by casting each byte to u64 before shifting. Also fix
the misaligned break statement while we are here.

Example of the result can be seen here:
Link: https://godbolt.org/z/zhY8d3595
It maybe not a real problem, but could be a issue in future.

Fixes: d499e9627d70 ("arm64/scs: Fix handling of advance_loc4")
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>