wifi: brcmfmac: add missing header include for brcmf_dbg

Including the fwil.h header file can lead to a build error:

drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil.h: \
	In function ‘brcmf_fil_cmd_int_set’:
drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwil.h:90:9: error: implicit \
	declaration of function ‘brcmf_dbg’ [-Werror=implicit-function-declaration]
   90 |         brcmf_dbg(FIL, "ifidx=%d, cmd=%d, value=%d\n", ifp->ifidx, cmd, data);
      |         ^~~~~~~~~

The error is often avoided because the debug.h header file is included
before the fwil.h header file.

This makes sure the header include order is irrelevant by explicitly adding the
debug.h header.

Fixes: 31343230 ("wifi: brcmfmac: export firmware interface functions")
Signed-off-by: Marcel Hamer <marcel.hamer@windriver.com>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20241211133618.2014083-1-marcel.hamer@windriver.com