tpm: constify transmit data pointers

Making cmd_getticks 'const' introduced a couple of harmless warnings:

drivers/char/tpm/tpm_tis_core.c: In function 'probe_itpm':
drivers/char/tpm/tpm_tis_core.c:469:31: error: passing argument 2 of 'tpm_tis_send_data' discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  rc = tpm_tis_send_data(chip, cmd_getticks, len);
drivers/char/tpm/tpm_tis_core.c:477:31: error: passing argument 2 of 'tpm_tis_send_data' discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]
  rc = tpm_tis_send_data(chip, cmd_getticks, len);
drivers/char/tpm/tpm_tis_core.c:255:12: note: expected 'u8 * {aka unsigned char *}' but argument is of type 'const u8 * {aka const unsigned char *}'
 static int tpm_tis_send_data(struct tpm_chip *chip, u8 *buf, size_t len)

This changes the related functions to all take 'const' pointers
so that gcc can see this as being correct. I had to slightly
modify the logic around tpm_tis_spi_transfer() for this to work
without introducing ugly casts.

Cc: stable@vger.kernel.org
Fixes: 5e35bd8e06b9 ("tpm_tis: make array cmd_getticks static const to shink object code size")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

drivers/char/tpm/tpm_tis.c

@@ -223,7 +223,7 @@ static int tpm_tcg_read_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
 }
 
 static int tpm_tcg_write_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
-			       u8 *value)
+			       const u8 *value)
 {
 	struct tpm_tis_tcg_phy *phy = to_tpm_tis_tcg_phy(data);