net: qed: correct qed_hw_err_notify() prototype

Change the prototype of qed_hw_err_notify() with the following:
* constify "fmt" argument according to printk() declarations;
* anontate it with __cold attribute to move the function out of
  the line;
* annotate it with __printf() attribute;

This eliminates W=1+ warning:

drivers/net/ethernet/qlogic/qed/qed_hw.c: In function
‘qed_hw_err_notify’:
drivers/net/ethernet/qlogic/qed/qed_hw.c:851:3: warning: function
‘qed_hw_err_notify’ might be a candidate for ‘gnu_printf’ format
attribute [-Wsuggest-attribute=format]
 len = vsnprintf(buf, QED_HW_ERR_MAX_STR_SIZE, fmt, vl);
 ^~~

as well as saves some code size:

add/remove: 0/0 grow/shrink: 2/4 up/down: 40/-125 (-85)
Function                                     old     new   delta
qed_dmae_execute_command                    1680    1711     +31
qed_spq_post                                1104    1113      +9
qed_int_sp_dpc                              3554    3545      -9
qed_mcp_cmd_and_union                       1896    1876     -20
qed_hw_err_notify                            395     352     -43
qed_mcp_handle_events                       2630    2577     -53
Total: Before=368645, After=368560, chg -0.02%

__printf() will also be helpful with catching bad format strings
and arguments.

Signed-off-by: Alexander Lobakin <alobakin@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>