Fix compilation error for nRF52805

[eupn]

When trying to build with nrf52805 feature, I got the following error:

error[E0599]: no variant or associated item named `SWI5_EGU5` found for enum `Interrupt` in the current scope
  --> .../nrf-softdevice-0.1.0/src/critical_section_impl.rs:26:25
   |
26 |     | (1 << (Interrupt::SWI5_EGU5 as u8));
   |                         ^^^^^^^^^
   |                         |
   |                         variant or associated item not found in `Interrupt`
   |                         help: there is a variant with a similar name: `SWI0_EGU0`

For more information about this error, try `rustc --explain E0599`.
error: could not compile `nrf-softdevice` (lib) due to 1 previous error

The fix verified to work in hardware on a nRF52805-based board.