net/mlx5_core: Use accessor functions to read from device memory

Use ioread function to read health buffer data. In addition, print the
firmware version as a string for readability and also use dev_err to have
the device string to be printed.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>