wifi: ath11k: fix NULL dereference in ath11k_qmi_m3_load()

In the Linux kernel, the following vulnerability has been resolved: wifi: ath11k: fix NULL dereference in ath11k_qmi_m3_load() If ab->fw.m3_data points to data, then fw pointer remains null. Further, if m3_mem is not allocated, then fw is dereferenced to be passed to ath11k_err function. Replace fw->size by m3_len. Found by Linux Verification Center (linuxtesting.org) with SVACE.