RISC-V: KVM: Remove unnecessary HGATP csr_read

RISC-V: KVM: Remove unnecessary HGATP csr_read

The HGATP has been set to zero in gstage_mode_detect(), so there
is no need to save the old context. Unify the code convention
with gstage_mode_detect().

Reviewed-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>
Link: https://lore.kernel.org/r/20250821142542.2472079-3-guoren@kernel.org
Signed-off-by: Anup Patel <anup@brainfault.org>