i2c: ismt: Fix undefined behavior due to shift overflowing the constant

Fix:

  drivers/i2c/busses/i2c-ismt.c: In function ‘ismt_hw_init’:
  drivers/i2c/busses/i2c-ismt.c:770:2: error: case label does not reduce to an integer constant
    case ISMT_SPGT_SPD_400K:
    ^~~~
  drivers/i2c/busses/i2c-ismt.c:773:2: error: case label does not reduce to an integer constant
    case ISMT_SPGT_SPD_1M:
    ^~~~

See https://lore.kernel.org/r/YkwQ6%2BtIH8GQpuct@zn.tnic for the gory
details as to why it triggers with older gccs only.
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Seth Heasley <seth.heasley@intel.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-ismt.c

@@ -145,8 +145,8 @@
 #define ISMT_SPGT_SPD_MASK	0xc0000000	/* SMBus Speed mask */
 #define ISMT_SPGT_SPD_80K	0x00		/* 80 kHz */
 #define ISMT_SPGT_SPD_100K	(0x1 << 30)	/* 100 kHz */
-#define ISMT_SPGT_SPD_400K	(0x2 << 30)	/* 400 kHz */
-#define ISMT_SPGT_SPD_1M	(0x3 << 30)	/* 1 MHz */
+#define ISMT_SPGT_SPD_400K	(0x2U << 30)	/* 400 kHz */
+#define ISMT_SPGT_SPD_1M	(0x3U << 30)	/* 1 MHz */
 
 
 /* MSI Control Register (MSICTL) bit definitions */