arm64: Remove a redundancy in sysreg.h

commit d38338e396ee0571b3502962fd2fbaec4d2d9a8f upstream.

This is really trivial; there is a dup (1 << 16) in the code

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Stefan Traby <stefan@hello-penguin.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>