wifi: rtw89: sar: do not assert wiphy lock held until probing is done

rtw89_sar_set_src() may be called at driver early init phase when
applying SAR configuration via ACPI. wiphy lock is not held there.

Since the assertion was initially added for rtw89_apply_sar_common() call
path and may be helpful for other places in future changes, keep it but
move it under RTW89_FLAG_PROBE_DONE test.

Found by Linux Verification Center (linuxtesting.org).

Fixes: 88ca3107 ("wifi: rtw89: sar: add skeleton for SAR configuration via ACPI")
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250604161339.119954-2-pchelkin@ispras.ru