seq_buf: Fix kernel documentation

seq_buf: Fix kernel documentation

There are plenty of issues with the kernel documentation here:
  - misspelled word "sequence"
  - different style of returned value descriptions
  - missed Return sections
  - unaligned style of ASCII / NUL-terminated / etc
  - wrong function references

Fix all these.

Link: https://lkml.kernel.org/r/20240215152506.598340-1-andriy.shevchenko@linux.intel.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>