rtl8xxxu: Implement IQK calibration for 8192eu

8192eu has it's own IQK calibration procedure, and notably uses
undocumented RF register 0x56 in the process.
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_regs.h

@@ -1130,6 +1130,7 @@
 #define RF6052_REG_T_METER_8723B	0x42
 #define RF6052_REG_UNKNOWN_43		0x43
 #define RF6052_REG_UNKNOWN_55		0x55
+#define RF6052_REG_UNKNOWN_56		0x56
 #define RF6052_REG_S0S1			0xb0
 #define RF6052_REG_UNKNOWN_DF		0xdf
 #define RF6052_REG_UNKNOWN_ED		0xed