tg3: Add error reporting to tg3_phydsp_write()

This patch adds error reporting to the tg3_phydsp_write() function and
converts a few more locations to use this function over the inlined
equivalent.

Reviewed-by: Benjamin Li <benli@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>