KVM: arm64: debug: fix kernel-doc warnings

KVM: arm64: debug: fix kernel-doc warnings

Change one "/**" comment to a common "/*" comment since the comment
is not in kernel-doc format.
Add description for the @vcpu function parameter.

These changes prevent warnings:

debug.c:27: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * save/restore_guest_debug_regs
debug.c:27: warning: missing initial short description on line:
 * save/restore_guest_debug_regs
debug.c:149: warning: Function parameter or struct member 'vcpu' not described in 'kvm_arm_reset_debug_ptr'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: James Morse <james.morse@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Zenghui Yu <yuzenghui@huawei.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: kvmarm@lists.linux.dev
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
Link: https://lore.kernel.org/r/20240117230714.31025-2-rdunlap@infradead.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>