thermal: mtk_thermal: Staticise a number of data variables

Sparse throws following warnings:
drivers/thermal/mtk_thermal.c:186:11: warning: symbol 'mt8173_bank_data' was not declared. Should it be static?
drivers/thermal/mtk_thermal.c:193:11: warning: symbol 'mt8173_msr' was not declared. Should it be static?
drivers/thermal/mtk_thermal.c:197:11: warning: symbol 'mt8173_adcpnp' was not declared. Should it be static?
drivers/thermal/mtk_thermal.c:201:11: warning: symbol 'mt8173_mux_values' was not declared. Should it be static?
drivers/thermal/mtk_thermal.c:204:11: warning: symbol 'mt2701_bank_data' was not declared. Should it be static?
drivers/thermal/mtk_thermal.c:208:11: warning: symbol 'mt2701_msr' was not declared. Should it be static?
drivers/thermal/mtk_thermal.c:212:11: warning: symbol 'mt2701_adcpnp' was not declared. Should it be static?
drivers/thermal/mtk_thermal.c:216:11: warning: symbol 'mt2701_mux_values' was not declared. Should it be static?

Make these variables as static to fix these warnings.

Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>