perf/x86/intel/bts: Rename local bts_buffer variables for clarity

perf/x86/intel/bts: Rename local bts_buffer variables for clarity

Rename struct bts_buffer objects from 'buf' to 'bb' to improve the
readability when accessing the structure's 'buf' member. For example,
'buf->buf[]' becomes 'bb->buf[]'.

Indent line 327 using tabs to silence a checkpatch warning.

No functional changes intended.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250407085253.742834-2-thorsten.blum@linux.dev