wifi: rtw89: phy: fix uninitialized variable access in rtw89_phy_cfo_set_crystal_cap()

wifi: rtw89: phy: fix uninitialized variable access in rtw89_phy_cfo_set_crystal_cap()

In the rtw89_phy_cfo_set_crystal_cap() function, for chips other than
RTL8852A/RTL8851B, the values read by rtw89_mac_read_xtal_si() are
stored into the local variables sc_xi_val and sc_xo_val. If either
read fails, these variables remain uninitialized, they are later
used to update cfo->crystal_cap and in debug print statements. This
can lead to undefined behavior.

Fix the issue by initializing sc_xi_val and sc_xo_val to zero,
like is implemented in vendor driver.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 8379fa611536 ("rtw89: 8852c: add write/read crystal function in CFO tracking")
Signed-off-by: Alexey Velichayshiy <a.velichayshiy@ispras.ru>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20260323140613.1615574-1-a.velichayshiy@ispras.ru