aarch64: camellia: Only use the lower 32 bit of an int parameter

* cipher/camellia-aarch64.S: Use 'w3' instead of 'x3'.

The keybits parameter is declared as int, and in those cases, the
upper half of a register is undefined, not guaranteed to be zero.

• Signed-off-by: Martin Storsjö <martin@martin.st>