wifi: ath11k: initialize 'ret' in ath11k_qmi_load_file_target_mem()

smatch flagged the following issue:

drivers/net/wireless/ath/ath11k/qmi.c:2401 ath11k_qmi_load_file_target_mem() error: uninitialized symbol 'ret'.

The reality is that 'ret' is initialized in every path through
ath11k_qmi_load_file_target_mem() except one, the case where the input
'len' is 0, and hence the "while (remaining)" loop is never entered.
But to make sure this case is also handled, add an initializer to the
declaration of 'ret'.

No functional changes, compile tested only.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240504-qmi_load_file_target_mem-v1-2-069fc44c45eb@quicinc.com