x86/entry/compat: Combine return value test from syscall handler

Move the sysret32_from_system_call label to remove a duplicate test of
the return value from the syscall handler.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230721161018.50214-4-brgerst@gmail.com