nrf_wifi: Update RPU patch to rev#8b918fb0a2d

UMAC:
     [SHEL-3248]: Support for EAP-TLS-SHA256 security type
                  in display scan.
     [SHEL-3251]: Limiting maximum transmit power from 40dBm
                  to 31 dBm as per hardware limitation.

Signed-off-by: Karun Kumar Eagalapati <[email protected]>

Author: karun2796