Fix the following warnings:
[Warning] hal_ssi.h@28,85: suggest braces around empty body in an 'if' statement [-Wempty-body]
[Warning] spi_api.c@87,27: comparison between signed and unsigned integer expressions [-Wsign-compare]
[Warning] spi_api.c@76,14: unused variable 'MaxSsiFreq' [-Wunused-variable]
Signed-off-by: Tony Wu <tonywu@realtek.com>
Fix hundreds of excessive compiler warnings due to out of enum type range
Examples shown as follows:
mbed-os.lib/targets/TARGET_Realtek/TARGET_AMEBA/sdk/soc/realtek/8195a/fwlib/hal_i2c.h", Line: 329, Col: 34
mbed-os.lib/targets/TARGET_Realtek/TARGET_AMEBA/TARGET_RTL8195A/PinNames.h", Line: 172, Col: 11
Signed-off-by: Tony Wu <tonywu@realtek.com>