x86/sev-es: Remove subtraction of res variable
vc_decode_insn() calls copy_from_kernel_nofault() by way of
vc_fetch_insn_kernel() to fetch 15 bytes max of opcodes to decode.
copy_from_kernel_nofault() returns negative on error and 0 on success.
The error case is handled by returning ES_EXCEPTION.
In the success case, the ret variable which contains the return value is
0 so there's no need to subtract it from MAX_INSN_SIZE when initializing
the insn buffer for further decoding. Remove it.
No functional changes.
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Joerg Roedel <jroedel@suse.de>
Link: https://lkml.kernel.org/r/20210223111130.16201-1-bp@alien8.de