wifi: ath12k: Replace band define G with GHZ where appropriate

wifi: ath12k: Replace band define G with GHZ where appropriate

Currently, band define and enum are with the word 'G'. Replace it with
more appropriate 'GHZ' for clarity and correctness.

No functional changes. Only compile tested.

Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Signed-off-by: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
Link: https://patch.msgid.link/20250324062518.2752822-5-quic_periyasa@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>