rtl8195am - fix spi_api.c warnings

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 <[email protected]>

Author: tung7970

targets/TARGET_Realtek/TARGET_AMEBA/TARGET_RTL8195A/spi_api.c

@@ -65,20 +65,18 @@ void spi_init (spi_t *obj, PinName mosi, PinName miso, PinName sclk, PinName sse
 {
     SSI_DBG_ENTRANCE("spi_init()\n");
 
-    uint32_t ssi_mosi, ssi_miso, ssi_peri;
+    int ssi_mosi, ssi_miso, ssi_peri;
     uint8_t  ssi_idx, ssi_pinmux;
     PHAL_SSI_ADAPTOR pHalSsiAdaptor;
     PHAL_SSI_OP pHalSsiOp;
 
     _memset((void*)obj, 0, sizeof(spi_t));
     obj->state = 0;
-    uint32_t SystemClock = SystemGetCpuClk();
-    uint32_t MaxSsiFreq  = (SystemClock >> 2) >> 1;
 
     /* SsiClockDivider doesn't support odd number */
 
-    DBG_SSI_INFO("SystemClock: %d\n", SystemClock);
-    DBG_SSI_INFO("MaxSsiFreq : %d\n", MaxSsiFreq);
+    DBG_SSI_INFO("SystemClock: %d\n", SystemGetCpuClk());
+    DBG_SSI_INFO("MaxSsiFreq : %d\n", SystemGetCpuClk() >> 3);
 
     ssi_mosi = pinmap_peripheral(mosi, PinMap_SSI_MOSI);
     ssi_miso = pinmap_peripheral(miso, PinMap_SSI_MISO);

targets/TARGET_Realtek/TARGET_AMEBA/sdk/soc/realtek/8195a/fwlib/hal_ssi.h

@@ -24,8 +24,9 @@ extern u32 SSI_DBG_CONFIG;
 
 
 #define SSI_DBG_ENTRANCE(...)  do {\
-    if (unlikely(SSI_DBG_CONFIG & DBG_TYPE_ENTRANCE)) \
+    if (unlikely(SSI_DBG_CONFIG & DBG_TYPE_ENTRANCE)) { \
         DBG_SSI_INFO(IDENT_FOUR_SPACE ANSI_COLOR_GREEN __VA_ARGS__ ANSI_COLOR_RESET); \
+    } \
 }while(0)
 
 #define SSI_DBG_INIT(...)  do {\