docs: KVM: Fix register ID of SPSR_FIQ

Fixes the register ID of SPSR_FIQ.

SPSR_FIQ is a 64-bit register and the 64-bit register size mask is
0x0030000000000000ULL.

Fixes: fd3bc912 ("KVM: Documentation: Document arm64 core registers in detail")
Signed-off-by: Takahiro Itazuri <itazur@amazon.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230606154628.95498-1-itazur@amazon.com


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>