scsi: fcoe: Use sysfs_match_string() over fcoe_parse_mode()

scsi: fcoe: Use sysfs_match_string() over fcoe_parse_mode()

Instead of copying @buf into a new buffer and carefully managing its
newline/null-terminating status, we can just use sysfs_match_string() as it
uses sysfs_streq() internally which handles newline/null-term:

|  /**
|   * sysfs_streq - return true if strings are equal, modulo trailing newline
|   * @s1: one string
|   * @s2: another string
|   *
|   * This routine returns true iff two strings are equal, treating both
|   * NUL and newline-then-NUL as equivalent string terminations.  It's
|   * geared for use with sysfs input strings, which generally terminate
|   * with newlines but are compared against values without newlines.
|   */
|  bool sysfs_streq(const char *s1, const char *s2)
|  ...

Then entirely drop the now unused fcoe_parse_mode(), being careful to
change if condition from checking for FIP_CONN_TYPE_UNKNOWN to < 0 as
sysfs_match_string() can return -EINVAL. Also check explicitly if
ctlr->mode is equal to FIP_CONN_TYPE_UNKNOWN -- this is probably preferred
to "<=" as the behavior is more obvious while maintaining functionality.

To get the compiler not to complain, make fip_conn_type_names const char *
const. Perhaps, this should also be done for fcf_state_names.

This also removes an instance of strncpy() which helps [1].

Link: https://github.com/KSPP/linux/issues/90
Cc: <linux-hardening@vger.kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20231212-strncpy-drivers-scsi-fcoe-fcoe_sysfs-c-v2-1-1f2d6b2fc409@google.com
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>